I have used sanding mops for years. I have one that is practically worn out that used to be a 220 grit but it is more like 1000 grit now and it makes very soft relief on the edges of what I cut. I use an old fan motor with a very long shaft and on that I put a jacobs chuck on it. The motor turns around 1000 rpm. It's ugly but it works hehe. I periodically add a couple of strips of 220 to the mix. For sanding of fretwork and the like with gentle care you get outstanding results. If you do not have one it is well worth the expense to set up a dedicated unit for it in my opinion.
DW