A very neat idea, although the execution isn't quite perfect.
Firstly the cloth seems to leave some fibres behind. These seem to reduce after a few uses, but definitely not something you want on the inside of your instrument.
The second issue is that the mop size is slightly too narrow to effectively brush the trumpet leadpipe. This is okay it just means going up and down a few times.
A neat product; I would buy again but only because there isn't an alternative on the market.