I have only used CrossBreed for 9mm sized Glocks and Alien Gear for my Shield (the older one without the neoprene backing). Out of the two, CrossBreed, hands down. It is more comfortable than the Alien Gear and the gun fits better in the CrossBreed, although given that the CrossBreed is for a Glock and the Alien Gear is for a Shield, I don't know if the comparison is completely valid. The Alien Gear seems to allow the gun to move front-to-back quite a bit when holstered. Retention is good, but the gun has some movement. I really can't explain why the Alien Gear is less comfortable, it just is. That said, the Alien Gear is still more comfortable than a lot of other holsters I have tried and would be a good choice if on a budget. If I had it to do over, I would have bought a CrossBreed for my Shield, but I was happy enough with the Alien Gear that I didn't send it back and still use it during the summer months when I carry my Shield.
Bub75