The USB Overdrive is free to try. You can download it and install it on your Mac to see if it fits your needs. If it does, you can easily and safely buy it from the online web store. If it doesn’t, the built-in uninstaller can remove the Overdrive from your system.
There are no feature limitations and no time limits in the unregistered version. The only annoyances are a gentle reminder at login and a short countdown when you open the user interface. I know that these things can be boring, but they allow me to keep working on the Overdrive.
But why should you pay for a device driver in the first place?
I’d love to give things away for free but writing software requires a lot of time and effort, not to mention the cost of all the USB devices I buy to make sure they work properly. I’ll post a picture of my office someday, my friends call it the Mouseoleum. I also have a family to feed, so you know your money won’t be wasted.
The USB Overdrive has been around for 25 years now and the original registration codes are still accepted. I only asked for a voluntary upgrade fee in 2008 when I rewrote everything from scratch for OS X. I may do this again for an upcoming major release, but you can rest assured that your license will not expire.