I also have heard great things, and everyone who uses them seems to like them.
Two points of consideration that I have heard with their use is maintaining a proper heat gradient and humidity levels.
Every breeder I have spoken to that uses them has told me they have a heated room and sometimes use humidifiers to maintain the proper conditions.
Right now I am looking for racks for college (easy to dismantle and transport). In addition to Freedom Breeders you may want to look into Vision Racks and ARSCaging.com
Though for adult boas (over 5ft.) you will probably have to go with Freedom Breeder to house the large animals. The other two seem good for CB-70 bins.
I don't know exactly what you are looking for, but I currently use only Boaphile Plastics cages and I love them for adult boas.
I am just looking for racks to make taking them to and from school easier than lugging a bunch of big cages.