I agree with LBF, those ones switch themselves off once tank water reaches the predetermined temperature.
The undergravel heaters, as far as I know, are the small 5w 'betta bowl' heaters. Non-adjustable and will always heat the water 5 degrees above room temperature. Not the best idea, I am using one myself for my QT tank but that is being monitored heavily with a seperate thermometer to ensure no massive temperature fluctuations.
I am preparing for the summer myself, I will be repositioning my guys into the laundry which remains cool through the summer. As it is easier to heat the tanks, than cool.
Beaten to it by LBF again. I use AquaOne products myself, the 25w is the smallest adjustable heater you will find. You can also pick up a 24L (6g) tank for around $30 from them also. My tip with using them is to position them horizontally for stable temperature.
Where are you located by the way? If you're Sydney area, I strongly suggest Aquaristic. Suggested to me by LBF. Extremely exotic Betta's each in 2g, clean, helpful. You'll be able to pick up everthing you need for under $200. I went with tank, hang on filter, heater, substrate, driftwood with anubias already grown in, water conditioner and the fish.
You can always shop around, but I've been to about 5 or 6 aquariums in Sydney area now and they are by far the best.
PS. I'm pretty sure a 25w heater won't fit into a 1.1g. It's 18cm long, so unless you increase your tank size, you may only be able to go with a 5w unadjustable.