Is SLOW-PCfighter safe?

The application was reviewed earlier in the year. https://www.virustotal.com/file-scan/report.html?id=64baccbd14fdeb7cf4c21942e06855035f3c1a54d4882bbf43cfc8b64150e980-1296742281

At this time I do not believe that it qualifies as malware, spam, or phishing. Having said that, it appears that it requires a paid subscription after the trial period. If you insist on using a registry cleaner there are free options that we will suggest if you are interested. However, I don't support the use of so called "registry cleaners" because they can aggravate a situation and take steps we are many times not manually aware of.  It is better not to resort to such programs if you don't know what is happening with the proposed fix and the registry. Otherwise, a change to the registry can make a system unbootable by one mistake.

Here are some good discussions:

http://windows.microsoft.com/en-US/windows-vista/Are-registry-cleaners-necessary
http://aumha.net/viewtopic.php?t=28099
http://cwsandiego.com/2010/11/16/registry-cleaners-proceed-with-caution/
http://blogs.technet.com/b/markrussinovich/archive/2005/10/02/registry-junk-a-windows-fact-of-life.aspx
http://www.whatthetech.com/2007/11/25/do-i-need-a-registry-cleaner/
http://billpstudios.blogspot.com/2007/04/do-i-need-registry-cleaner.html

If you absolutely must use a registry cleaner, always backup the registry first:
http://windows.microsoft.com/en-us/windows7/Back-up-the-registry