The intro+ would be the lowest price (100$) with the best features. The herpstat 1 is a great all round one for an extra 40%. The HS2 and HS4 have 2 and 4 probes so will control 2 or 4 separate devises. Herpstats are cheater than the competition I don't know REBELLMORPH is on about. Unless you are comparing a on/off stat? There is a world of difference between them. Buy a good quality t-stat and save vet bills!