Edit: I saw this quote on the Mackeeper website you linked (it is good design) "MacKeeper was noticed at Macworld by a journalist from Cult of Mac". So I chased that phrase and all I found was algorithmic page generators like this http://drgogek.com/is/is-mackeeper-really-a-scam-cult-of-mac....
Using a different tack CoM mention Mackeeper in a single page found from their search box, an affiliate promotion page ... using Google unearths more promotions, https://www.google.co.uk/search?q=site%3Acultofmac.com mackeeper.
So, it looks like their quoted reviews are from people they're paying to sell the product, that's a warning sign.
Didn't investigate further.
http://www.imore.com/avoid-mackeeper
> What's more, "uninstalling" MacKeeper doesn't get rid of all of it — you'll find various traces of it in your Mac's system library folder, and they take a bit to get rid of (just search for anything with zeobit or MacKeeper in the name, and you'll turn up files).
Since then, a few of my friends, who aren't into tech, almost installed MacKeeper. They all had a long history of using Windows and felt that installing some Anti-Virus, Anti-Malware junk was the most natural thing. For normal users it's really hard to distinguish between legitimate applications/websites and shady stuff.