OP got a "No" option?? I [expletive removed] didn't
So let's start my venting.
Apart from your latest version 5.51.6939 that did NOT indicate anywhere about being the Trial version before downloading and installing it, add these gems to your Hate Mail list:
a. Which idiot there authorised the same filename for both Trial and Free versions - the same QA Manager that let old versions be released under new version filenames on more than one occasion over the past few of years perchance?
b. When the Trial version first opens it shows the box asking to sign up to the Trial version.
WHICH YOU CAN'T [expletive removed] CLOSE UNLESS YOU KILL IT USING THE TASK MANAGER!
Whose bright idea was that, pray tell?
c. Flushed that Trial version out of the system (Gee, isn't Glarysoft's Glary Utilities handy for that?...), went to your "https://www.ccleaner.com/ccleaner/builds" site and down'd the free "Standard installer" file.
As an aside, just why the [expletive removed] did you have to detail acquiring the Slim version to the OP there?
Anyway, installed what I downloaded, had a quick peek into the WinDoze Startup and there's now an interesting entry called "CCleaner64.exe /MONITOR"
"Monitor"?? Curiously I did not see anything during the reinstall asking whether any background monitoring was requested.
So whose bright idea was that to surreptitiously install that function??
Piriform seriously copped a slap around the head 'n shoulders last time they tried that [expletive removed], so let's see how many more users you lose continuing on with these antics.