I have the Mini Hydor heater, love it its like a little heating pad, they are preset and it keeps my 3 gal at 75 degrees which is what I want as I don't want higher for my bettas.
I did have the marineland one you talked about a few years ago, it was not very reliable and quit working all together 1 year later.
I hope this Hydor is a good one, time will tell. They can be buried if you want to or stuck to the back of the glass. I have mine stuck to the back of the glass as my background is black and you don't see it.