I have them right now in my 10G, I got the 75W version and it alsmost fit my whole tank (Bottom almost touching the gravel) Also this is the tank I have (http://www.petsmart.com/product/inde...AvailInUS%2FNo
It works really well, and the calibration is really easy to do. Just read the instruction and it should be a breeze, it was for me lol. But if you want something short, get the Hydor Theo, but if you don't mind the size, and wants one of the best, Eheim Jager is one of the best for AQ heaters. I did a lot of research before purchasing this lol. Either Eheim Jager or Hydor, you can't go wrong!