I'm a big fan of wire-it-yourself dual ranco ETC111000.
I recommend dual thermostats wherever you have more than 10 animals on it.
I use them for everything.They don't have all the fancy features of the helix and herpstat, but they are less likely to fail.
I have 4 rancos controlling my ARS 7030 rack, 2 on my freedom breeder large reptile compact, 2 on a homemade juvenile rack, and 2 on my hibernation rack in a cold cold basement. I also keep a double ranco all set up as a spare, just in case.
Yeah, I'm paranoid. But it's a better affliction than burying a dozen cooked pets, having a house fire, or paying for a vet appointment for a dozen sick snakes.
The absolute best would be a wire-it-yourself ranco 111000 as a backup with a high quality proportional like a helix or herpstat.
If the helix fails and goes full throttle, the ranco will kick in at a 2 degree higher setpoint, and kill power to the helix.
Taking it further yet, I have a quad ranco setup on my ARS 7030.
I have 2 6" wide E-series heaters on each level. (I have no idea what size heat tape is under there, I just know it takes 3 wire plugs, each strip is metal on top and covered with reflectix insulation on the bottom.) The metal acts as a heatsink or a heat reservoir, and the reflectix insures that the heat fires up, not down.
If 1 thermostat goes cold, I have the other tape. If one ranco goes full throttle, the one before it kicks in at a 2 degree higher setpoint and keeps it from getting uncomfortable.
Those heaters together heat a 12" wide swatch of the 33" deep tub, and the snakes seem to LOVE it.
Instead of a teeny hot spot the snake has to cram into, it's a 12"x16" area of gentle warmth.