A recent article in PCA indicated that registry cleaners do little to speed up a PC. Whether this is the perception of a user or not is a different question - I believe it helps to remove the rubbish.
I have used WinASO and found it good but awkward with 10 entries at a time with the trial version. As a result I have used Ccleaner (which is full and free) for some time and found it fits the bill.
As for an (apparently) unsolicited download showing large numbers of files/entries to be cleaned, this is not unusual where a software supplier wants to make a sale - or worse still, malware wants to get itself installed!!