It's extremely expensive per unit ($20).

Though there is a benefit from the heating coil component in some areas at some time of year, it's hard to get over the price vs. the marginal benefit that gives in all but the cooler times of year.

Also, the heating coil is rather small...and it seems to run all the time rather than turn off when soil temperatures could get too warm.

I suppose you are right. But what aboit if you were using it for a few indoor plants rather than a hole raised bed. I mean it is expensive but you would think i would be more benifical for the plant in an consistent tempatured environment.