Most freebies will do that to 'entice' you to purchase.
Most AV programs like Norton or McAfee are free from your internet carrier and can clean your registry too.
I double duty with Norton & Microsoft Security Essentials - both do your registry.
I also use {Free} CCleaner, one of the few free reg cleaners that 'works' for you.
Get it here:
http://www.piriform.com/ccleaner/downloadIn essence I triple clean. I need my system relatively clean for programming. And, the above suit me very nicely & without expense.
Note: Reg cleaning for most is simply for broken reg links and such left over from old programs, some web sites [malicious or not] & even AV programs.
As posted above you may not need to clean your Reg. And if you do you should know how to "Fix" it. If you don't understand reg code then going in manually is a very bad idea.
I would suspect your slow problem is more related to adware or malware. Go after those first with a good AV program as above. Use multiple ...ware cleaners and run several times.
I use the reg cleaners because I'm constantly effecting my reg files. If I have to, I could go in manually. They save me time, unless of course I have to repair one. Which btw has never happened.