We built it ourselves and, at the time, it was a lot cheaper than buying a heaterstat. It just heats that one tank. The tank at the other end of the house also sits on a heat pad. Both are 4ft x 2ft. The smaller tanks all have heaterstats.
A heatpad covers the whole base of the tank and heats evenly.
No unsightly heaterstat in the tank and big fish can't break it if it is not in the tank.
Being underneath the tank, with polystyrene under them, heat rises so more efficient.
Grant likes to build such things as a change from fixing computers
He has his electrician's ticket so knows what he is doing as well.