I only recommend heaters with an adjustable temperature dial--they have a dependable thermostat which will give you security, stability and control. Only a few people have conditions that are ideal for using pre-set heaters. Your house needs to have a fairly high, stable ambient temperature for them to be effective, and not everyone has that luxury. It's good to know your betta's tank temperature will not fluctuate if someone decides to turn up the heat or the air conditioning or if they accidentally leave a window open.
I recommend buying your supplies online whenever possible, the prices will usually be around $10 cheaper online than in a retail store and you don't find yourself supporting stores that mistreat their fish, lizards, birds, and other small animals. I do all my shopping here: http://www.fosterandsmithaquatics.co...lies/pr/c/3578
since they have a wide variety of quality items and offer very reasonable $8.99 flat rate shipping--so if you buy more than one item, you save enough to more than make up for the cost of shipping. It's the best way to get the supplies you need.