that method will suffice, many many brewers (including myself) did this for awhile. only thing is, like you had mentioned, the fermometer will suffer. and the temps will vary, this awesomely is not a full issue, it'll just be a tad more difficult to replicate a recipe if you loved it.
if you go to the fridge controlled method, you will need to turn it all the way to cold. and set the remp on the controller. the controller will not let the fridge run untill it gets above your set temp, then it'll allow the compressor to run to chill it back down. if that made sense.
you should go to the fridge method... just sayin!
it's a tonnnnnn easier. it's like ron popeal "jet set it, and forget it!"
mine changed my life... ACT NOW!