When acclimating your fish, you want to float your fish in a cup of its old tank water in the new tank water. This will help with the temperature adjustment. Add a teaspoon of the new tank water to the cup every 10-15 minutes for an hour. After you've done this, you should be able to gently release your fish into the tank.
However, you don't want to increase the temperature of the water more than 1 degree with in an hour. You want to make the new tank water as close to the temperature of the old tank water as possible, and then only turn the heat up one degree every hour. If you're at 76 degrees now, you would want to do this about 4 times.
I don't know about the quality of the Aqueon mini heater, but like I said, I use the 50 watt in a 1 gallon with absolutely no problem. It is adjustable, submersible, and it has automatic shut off so that, if working properly, it will shut itself off as soon as it reaches the desired temperature and it will turn itself back on when the temperature starts to decrease (by roughly half a degree or so). This would also be a good choice for a heater because in the event that you ever upgrade to a larger tank, this heater is made to heat up to 20 gallon tanks. It also has a lifetime warranty, should it stop working by no fault of your own.