Is the Mounting Master skill worth it?

Short answer: no.
Well... maybe sometimes.

Long answer

It's a shame there's so much lack of information about Aerial Style, since it's a genuinely fun and strong style.

I think most of this information blackout stems from the perception elitists have about this style being "weak and not viable".

"Not viable" for what? For time attacks? Who cares? Most of those elitists aren't viable players for time attacks, anyway.
And why people in Monster Hunter insist on blindly following whatever they say without trying things that aren't crtical cookie cutter sets?

Go kill things using aerial guns or bow, then come tell me they aren't "viable".

I have at least 800 hours on my back playing Aerial Style with all kind of weapons and I have effectively helped many, many teams and killed many EX deviants without carting using Aerial.
Of course it is a "viable" style.

Even though this style has its pros and cons, this post isn't about that, so I'm not going to talk about that anymore here. I'm just stating that if you like to play Aerial, go for it by any means; mainstream opinion be damned.

Anyway, let's go back to our main topic.

The problem with Mounting Master 

This skill does two things: it makes you mount faster and it makes you easier to topple a mounted monster. That sounds really great in theory, but in practice those two things it does have some serious design flaws features that make this skill irrelevant.

Not so faster mountings

Mounting a monster works the same way any other status in this game: each status attack adds some numbers to a hidden status number, once you surpass certain threshold number your status will be applied. Each time you successfully apply an status, that threshold gets higher.
In plain simple words: every mounting takes more hits to get applied than the one before.

It seems what Mounting Master does is adding more Mounting Status to each of your aerial hits.
I'll clarify this with an example.

Let's suppose you have a mounting threshold of 30 and any aerial attack you do without Mounting Master does 10 Mounting Status, while using it will give you 15. You have something like this:

Threshold: 30
Normal hit: 10
MM hit: 15

That means you need to hit 3 times before mounting if you aren't using MM, while it only takes 2 hits with it.
Hey, that's nice! You really mounted faster, but hold your horses.

Now the threshold has gone up and you have this:

Threshold: 90
Normal hit: 10
MM hit: 15

Now you need 9 normal hits, while 6 with MM. It's still a difference, but it's not so noticeable.

Next time:

Threshold: 250
Normal hit: 10
MM hit: 15

... and you understand this pattern.

I invented these numbers for illustration purposes (since I don't know the real numbers), so these numbers represent a sweet 30%, which would mean 30% more mountings per fight.
In practice, there are so few mountings per fight that even if that 30% was real, it would be negligible. What's the 30% of 5? Just 1.5.

That really checks with my experience.
In real life, Mounting Master only gives you 1 (2 at most) more mountings per fight. And I don't remember ever seen more than 4 mountings per fight.

In practice, Mounting Master will only make you get faster the first mount (and maybe the second) because the fight ends before you get too much mountings; the monster simply dies.

If you don't kill it outright with a mount, that is.

Is (maybe) getting just one more mounting per fight worth those 10 skill points? I don't think so.
I would rather use those points for more useful skills, depending on my weapon.

I personally think Evade Extender is a better use of skill points for Aerial, since it lets you bounce on the monster from farther away and it lets you easier get out of the way too.
Of course, that skill is not that useful if you are using an Insect Glaive, but you get the point.

And yes, I know most of you will say it's better to cram there the same old boring skills everybody suggest all the time (Razor Sharp, Handicraft, Weakness Exploit, Critical Boost, yadda yadda). I'm suggesting things few people have talked about before; no need to say what everybody is already saying.

Now let's go to the other problem with the way mounting works in MHGU.

It isn't that hard to topple a mounted monster, anyway

Once you get a mount, it starts a minigame when you press buttons to fill a gauge. Once that gauge is full, you topple the monster and everybody cheers in joy.

Then there's a big happy dancing party.

Mounting Master indeed makes this minigame easier, but I'm not sure why. I think it makes you fill faster that toppling gauge, but I feel it also gives you more margin of errror within that minigame.

You see, this minigame is all about when to press and when not to press buttons. If you mindlessly mash buttons as soon as you mount, the monster will topple YOU and you would waste the applied status.

It's really annoying when I make an effort to build up the mounting status, just for some idiot who doesn't know how to play this minigame win the mounting and promptly proceed to waste all that effort by getting thrown out in less than 2 seconds.

You only press buttons when the little head is green, you asshat!

Anyway, this minigame is all about knowing the movement patterns for the monster you just mounted. Every single monster has a different pattern of when to press buttons... and Mounting Master doesn't change this fundamental fact.

As I said, I feel like MM gives you some margin of error, so you can screw up a bit in this minigame and you won't get thrown away. But when you have perfectly nailed the monster patterns (and you should anyway), this feature of the skill also becomes irrelevant.
All in all, it's still a nice crutch to have while you are learning how to topple though. And I fully recomend the skill for that purpose.

See? This skill's two main functions aren't that great in practice, anyway.

What would Mounting Master be actually useful for?

I personally would recommend it only for two kind of players:

• The complete novice who wants to learn how to mount and topple.
• The Hame guy.

Yeah, you read right the last one.

If you don't know what "Hame" is, it just boils down to one person locking a monster in place while all the others unleash their fury on it. Killing it without it even touching anyone.
You apply statuses, KOs, and put traps to be able to do so.
It's really enjoyable to Hame assholes like Tigrex or Brachydios. If you have never done it, try it someday; you'll get great laughs.

Back to the point.
By the way it works, Mounting Master gets you the first mounting pretty fast but the next ones not so.
Since Hame is all about killing a monster fast, the whole party benefits quite a lot from getting a fast first mount... and you won't probably see a second mount anyway.

In fact, I have an armor setup I use for charm farming (Hame a G4 Brachydios) with a paralyzing Insect Glaive.
I made this setup before learning how to Hame using the LBG God's Isle and that's still my go to set when farm charming.
Using God's Isle is arguably a better and confortable way to Hame, since you can paralyze, sleep and KO with it, but it's really hard to succesfully pull the sleep bombing gig with randoms. So I changed the sleep with a mount and I have never had problems.

So, that's all for now.
I hope this has helped you and make you consider some uses for Mounting Master I haven't thought about (would love to hear your ideas in the comments).

Good hunting!