I bought this at the same as I ordered the HB Spalted Maple UkeBass as I felt I needed a thumb rest and did not want to glue or screw one on permanently.
As the thumb rest clips over the sound hole, I did wonder if this would restrict playing close to the bridge, but it gives adequate coverage of whichever area you want to play.
The rest has a small amount of padded felt on one side, so you can be assured it won't leave any markings on your instrument if you remove it.
In my opinion, the pricing is a little on the steep side for something so simple, but there isn't anything on the market that I could find which does the same thing - and what it does, it does well.