I was looking for a wireless bluetooth mouse and found this one selling for $20. I bought it and tested it out and its pretty good and probably the best bluetooth mouse available in this price-range. Checked back up on it and see that MadCatz official store is also selling them for $20.
Be sure to download the Rat M "Office" driver rather than the regular Rat M driver if you end up buying it. And I don’t know what the reviewers are talking about but it works fine in Win 10, and the driver and configuration software works. I’d say it is great for regular use but would falter in gaming or precise Photoshop work.
Tagged Bluetooth 4.0 because no ’3.0′ tag