I just bought a 40 Breeder to set up for my reef. Reasons why I went with a breeder:
1. Lower!! I can probably pull off some corals without having to go metal Halide lighting and just use Power Compact
2. More room on bottom for aquascaping
3. I like the smaller fishes that stay around the live rock: Gobies, Clownfish, Wrasses
4. More live rock for more inverts!! Love the inverts!
5. Fit PERFECTLY on an old desk I am using for a stand
I am putting in about 30lbs of base rock and 40lbs of live rock to start with.
When I was at Petco last..they had a "Critter Cage" and a 40 Breeder Aquarium. The Critter Cage did seem thinner. It had a lock like thing on the cover. If your has that it is probably a critter cage...and it may no be a good idea. My 40 Breeder tank glass is 3/16" thick. Any smaller than that...you may be in trouble.
I will be starting my process in December. I have the tank and the cover (and the kids decorated it with window cling reef fish..I know...some are upside down...the 18 month old did those stickers and I can't bear to change it...I hope it doesn't happen when it is set up for real).