The hydor minis are rip-offs in my opinion. Depending on the ambient temperature of the room they don't get hot enough, and they don't keep the temperature stable. They also break really easily and if you accidentally leave them out of water while they're plugged in, they crack. I had these before I upgraded to the adjustable heater--I really wish I hadn't wasted my money on them.
Also the aquarium linked to this thread is--ew. You could easily get a much larger aquarium for that price, and it's poorly designed and too small to house a betta permanently--bettas kept in tanks that small often develop neurotic behaviors such as tail biting and glass surfing, become obese, and die from ammonia poisoning.