Mecha with switchable frames and multiple forms are staples of Mecha fiction. But, much like with Extra Areas, they have one glaring conceptual flaw that needs to be fixed before you adapt them to a point-buy effects-based system: You can already give your mech anything you want, there is no benefit to locking a flight mode or aoe weaponry behind a form that will only be useful some of the time.
My solution to this was to make Alternate Forms let you switch stats around by default, giving them a base benefit that justifies their purchase. The most obvious and probably most practical combination is to switch Systems and Speed, leaving one of them at 0 and investing your extra MP in the other. This gives you the benefits of a high mobility form and a long range utility form.
But of course, that wasn't going to be enough to make a plane form distinct from a humanoid form, or an artillery frame distinct from a submarine frame. I immediately wrote Superior Morphing to complement Alternate Forms and give them that something extra they needed to make each form or frame unique.
How'd that work out? Let's see.
Frames may not look like much at a glance, but Features make them a very efficient alternative to Antigravity. For 25 MP you get a land Frame and a space/underwater Frame which covers 90% of Operations. This will give you a +2 Defense from Defensive Terrain , lets you ignore Difficult Terrain and grants the ability to shoot over defensive formations. Each of your forms gets back 10 MP, so for 15 MP you've got half the effects of Antigravity (at no Energy cost) and a Defense boost to go with it. Then, if your game has more than a single mission in the third terrain type, you can Mid-Scene Upgrade for it with another 5 MP or just suck it up. The problem with this is that you don't have a convenient way around Extreme, Withering or (oddly enough) Sliding Terrain, but the +2 to Defense should make up for it.
This is a very effective Upgrade, but suffers from The Strong Adapt in the Expansion doing the same thing but better in nearly every way. The Strong Adapt requires you to not take Mid-Scene Upgrade though! You may know I've gone on record stating that Mid-Scene Upgrade is potentially the most exploitable ability in the game, so there's still a reason to use Frames.
Switching Features on the fly is really strong and easily worth the 10 MP cost, which is what Antigravity costs, but Transformation costs just 1 energy to activate (with Superior Morphing, at least) while antigravity costs 2. When you're not using the flight mode, you can use a Terrain Specialist or Extreme Adaptation Form, which is really handy. The balancing mechanism of this is that having to choose between those forms means sometimes you will have the wrong combination of Upgrades/Weapons/Attributes for the Terrain that you want, so it takes a bit of smart playing to get the most out of it.
Between that and the complexity of Alternate Forms in general, Transformers are not for beginners. This is especially true with Maneuverable Transformer encouraging you to switch back and forth every Turn and somehow not crippling yourself in the process.
In hindsight, perhaps the core mechanic for Alternate Forms should not have been switching Attributes, but switching Features instead, because Features are the iconic thing Alternate Forms do in fiction. Superior Morphing does this, but it costs extra MP and complicates things by requiring you to take another Upgrade. The current version has the benefit of being more powerful. Switching Upgrades, Weapons and Attributes gives you more room to optimize your build than if you just switched Upgrades and Weapons, after all. The problem is that you have to understand how it works first and Alternate Forms are one of the upgrade lines that confuse new players the most.
I think Alternate Forms are messy and complicated, both things I'm not fond of. But they work and the builds they enable are powerful while taking some skill to play, making them rewarding to use. I'm not sure how the complexity problem could have been fixed though. Perhaps there could have been pre-written Forms with their own benefits and drawbacks (sort of like Features) and you could just select between them instead of assembling the Forms yourself with Upgrades and Weapons. I'm not sure that would be better in practice, but it would be easier to understand at least.
I do like them overall though, and given how difficult they were to work with, I'm glad that their complexity isn't necessarily a bug but can be considered a Feature for players looking for a more difficult build.