I was changing the strings on my double bass and was recommended to get one of these to help speed up the process.
For the price, it's just not worth not having one and it made the job much quicker and easier.
Solidly made out of plastic, it makes very quick work of installing a new string or set of strings on your bass.
The string winder will also work on electric basses with 'Fender' style machine heads so I'll get more use out of it than I was originally expecting.
A very useful item to have in your gig bag or tool box.