"You can use VueScan on up to four different computers that you personally use, with any combination of operating systems, with any number of scanners, both x32 and x64, with a single license. If more than one person (who isn't a family member) uses the computer, then you need a separate VueScan license for each computer."
Generous terms and really good support.
I support FOSS and rarely buy stuff unless its quite special
Vuescan is not cheap cheap but its aye worth it.