I've heard good things about Helix. That said, take into consideration what kind of heat pads you're using. Are they the SAME brand and the SAME sizes? For example, two 10-20 gal Zoomed heat pads? Then, okay. As long as you're also considering Oren's input, you should be fine. But if you have, say, one 60 gallon Exo-Terra heat pad and one 10 gallon Zoomed heat pad, you're asking for serious trouble. Different sized heat pads take different amounts of electricity to get to the same temperature. Same with different brands--they aren't all built exactly the same, and that has to be taken in to consideration.. When I consolidated all of my adult/sub-adult corn snakes' 20L & 29 gal tanks to one thermostat, I even went to the trouble of buying a new heat pad for one so it matched the other three. I didn't want to accidentally cook "Hansel" just because there was some wiring difference between the Zoomed and All Living Things heat pads.
To elaborate on Oren's input, you should also consider location. They should be right next to each other for the most accurate control, and each should have their own digital thermometer to make 100% sure all goes well. I had two tanks on one thermostat at one point: a 20H and a 10, both with the same size/brand heat pad. The thermostat controlled the 10 perfectly (where the probe was), but the 20 could fluctuate pretty wildly depending on the time of day. It never got dangerous for the tank's occupant (obviously--the supposed "picky feeder" boa ate like a champ the entire time), but the variations (often going from 75*F to 90*F over the course of the day) were still a worry and certainly something to consider.