The Filco ones are the ones that have metal bars that a piece of plastic hooks onto, Leopold stabilizers look like they're two small "mini-cherry switches" on each side of the mx switch. I'm sure there's pictures out there, probably in the wiki.
When I say alpha keys, I mean the A-Z key. On my Noppoo, pressing any of the stabilizer keys feels pretty consistent with the "feel" or any letter keys, just bigger. On the Leopold, it just feels different. On the space bar you don't notice because it's so large and feels so different anyway just based on size. Honestly even the shifts, caps, and enter keys don't feel that noticeably different. The only one that stands out imo is the backspace. I have one of those "squeeky" backspaces and I'm pretty sure it's because of the stabilizer. It's not too bad if you hit if on center but since most people hit it off center with their pinky, it just lacks the "snap" of the other keys. I'm not sure how to describe it but I kinda think "wet newspaper" when I think of the backspace. As bad as that may make it sound, in reality it's not even that noticeable, at least to me, although your mileage may vary.
On the flip side, the pro of the Leopold style (or I guess I should call them Cherry corp style) stabilizer keys are they are no hassle uninstall/reinstall. You just pull on them with a keycap pull like any other key and you're done. Filco style can be a little tricky (had experience on em with my Noppoo). The best way to do it is to pull the key out so it snaps out of the cherry mx switch but still attached to the stabilizers and then "wedge em out" by pushing left or right on them to unsnap it. This can be really difficult if it's stuck on the switch good as you'll need to pull hard to dislodge it but pull too hard and you'll be pulling on the stabilizer. I'm so poor at doing this I often end up pulling the key completely off. Most times it'll pull off the plastic tab holding the metal frame that's connected to the key off the key and you just have to push it back in though sometimes it'll pull the metal hinge off completely or in one case it completely pulled off the stabilizer completely (two tiny pieces of plastic connected to the bottom plate). It wasn't hard to fix everything and put it back into place although I did have a mini-heart attack when I saw that. Also I can see if you are too rough or unlucky, you might permanently damage your keyboard this way.
