I've always used Johnsons on/offs for my flexwatt (for AP cages) and it's always worked wonderfully for me. I would recommend a Johnsons over a Hydrofarm, though. In my experience the Hydrofarms work just fine for some heaters, but I wouldn't use them for flexwatt because they tend to let the cage cool a bit more before turning on, whereas the Johnsons keep the cage within 2-3 degrees of the desired temp all the time.