I have one that I use with a heavy duty timer (like is used for outdoor Christmas lights) on a ground fault circuit. If you set it for about 5 hours of on time before you brew, it will have your stike water at the 160-170F range. You can quickly adjust and mash in first thing in the morning.
It goes into the HLT to heat the sparge water once it is done with the mash. Fire is used to get the sparge water to the final temp. Saves propane for sure.
Edit - 10 gallon batches for my example.