I'm glad to see that you got your betta in his new home. Don't get that heater. I bought that heater a few weeks ago and it didn't heat the water. Maybe it was a defective one, but I felt it was a cruddy product.
I got this heater http://www.petsmart.com/product/inde...ductId=3792732
. It's been working, keeping the temperature 76-80 degrees. I also have the same one gallon jar and the heater fits nicely inside. (I really need to post a picture)
Just make sure to get a thermometer to make sure your heater is working properly.