Been on lots of old work jobs where a flex bit would have saved a lot of drywall trenching and repairing.
I haven't gotten around to getting one of these because I figured the 36" one would be the most useful, but no one stocks that length. 54" and 72" seem to be everywhere.
36" is a whole lot easier to move around with and you can always the the extention shaft.
I've asked around here and no one has ever used one. Strange. They seem incredibly helpful.
