I installed the paid-for SlimClean Plus on my W10 system. It seemed to go ok - although I wouldn't know if it was really doing any good in any case - until it tried to get me to pay for their driver update feature. I uninstalled the separate routine that was asking for payment using windows uninstall. Then soon after, SlimClean started acting up, showing "analysing" and using up to 30% processor power continuously for over 24 hours, and I had to end it using task manager.
SlimClean helpdesk suggested two things to try: restore my PC back to a previous state; or uninstall and reinstall SlimClean. I tried the latter. No difference, as soon as it loaded, it showed "analysing" which continued overnight. Then I uninstalled, closed down, restarted and reinstalled. Still the same, still had to use task manager to close it down.
As for their first suggestion, if SlimClean can't cope with automatic updates of W10, then it is no use to me, I don't have the time, the inclination, nor indeed the knowledge to keep fiddling with restores etc because their software is not fit for purpose.
Cleverly, the software did not start to malfunction until after the 60 days refund period had expired.
Speaking with friends and colleagues, and looking at various websites, it looks as if these paid for "booster" or "cleaner" packages are a waste of money in any case, if you really want one, chose one of the freebies.