I have not used one, although I looked at and decided not to for the following reasons:
Complexity = more failure points
Complexity = harder to set for two guns rather than just having two custom fit holsters
Relatively bulky
Relatively expensive
Designed to be adaptable; therefore compromises doing the one thing it needs to do well: securely hold a single model gun in the safest, most secure and comfortable, smallest footprint, concealed method possible.
Others who have actually used the system may have different points of view. I look forward to hearing from proponents.
I love their Cloak Slide and Cloak Tuck 1.0 and 3.0. The Cloak Mod and now their Shape Shift are just to busy. The concept is good, and I've heard a lot of people really like them, but I'm a KISS kinda guy. Keep it simple......well, you know.
You might like the Foxx IWB holster. It is partially leather and much smaller and complex than the AlienGear. I had used the Aien Gear IWB for about 3 years before moving to Foxx. Much more adaptable too.
I ended up with an Alien Gear Cloak Tuck IWB (I believe the 3.0) because I needed a holster quick for my Glock 20 10mm when I went out to Idaho and Wyoming last year. The holster was inexpensive and served it's purpose well enough. I did some novice level hiking and found the heft of the G20 to be secure. However, the magazine carrier that came with the holster left a lot to be desired; it was too bulky and I resorted to carrying the spare magazine in my pocket.
Thanks for all the responses. After being unable to find an Alien Gear locally that I could look at & actually touch, I went with the Vedder Light Tuck iwb. So far, so good, I really like it.