I think I like Kritter Keepers. I recently bought one for my daughters fish. I bought a large (3gallons). That one is going to be a bit of a PITA to change the water weekly-it is too small to plant and cycle(IMHO I know it CAN be done but I want a more stable cycle) and too big to lug around for water changes @24lbs full of water. I wish I would have bought the medium(1.75 gallons) because 2x weekly 80% water changes are the schedule we are on. I think I'll use the large for a spawn tank(albeit it will be a bit small for my liking) and get her the medium.
Anyways, the ONLY thing I dislike are the lighting options. I may have to make an acrylic top because I had wanted to use a small desk lamp with a 6500K light so he could have plants. It doesn't look like the Kritter Keeper light is gonna cut it for plants.
Other than that they are cheap, crystal clear and cheap!
I'd recommend the x-large(6gallon) as a spawn tank or tank meant for plants or cycling, the LARGE for a hospital or spawn tank and the medium as regular quarters for 1 betta if you are getting it for a kid. 3 gallons is just an awkward size IMHO for a kid to manage. Yes more water is better but the trade off is the ease of handling a smaller tank 2x a week.