Thanks for the feedback, I'm the person at Red Gate currently kicking off the work to revamp our licensing and installation processes as we're fully aware they're not a great experience at the moment.
If you're also having issues with the menu items in SSMS or VS please do let us know. In SSMS for example going to Tools > Customize and deleting the Red Gate toolbar should help, but if SQL Prompt is still showing as a menu item it likely didn't completely uninstall, and therefore we'd be happy to look into what has gone wrong. If so please do email support at red-gate dot com with details of exactly what's left behind after uninstall. Many thanks.
However if you just had a poor experience uninstalling our software I'd like to apologise and assure you we're aware of the issues and looking to tackle them.