I am like brendanMcnelly said concerned with security and keeping my MBP smooth and fast.
Then MacKeeper is not for you.
Regarding the issue of keeping your machine running fast, have you actually done any benchmarks? If not, you probably just feel that MacKeeper makes your machine faster because it's been on there for so long. Perhaps you may have even had some corrupt caches that were causing a real problem, and that made MacKeeper's "cleaning" appear to work initially.
However, the kind of "cleaning" that MacKeeper, and other apps of its ilk, does is not something that is needed on a Mac. In fact, it can actually harm the performance of your machine, or if if gets a bit overzealous or suffers from an error, can damage your system.
For more information, see The myth of the dirty Mac.
As for security, MacKeeper offers only one real piece of security: the Avira anti-virus engine. You would do better, if you wanted to run that, to uninstall MacKeeper and install Avira itself, which is completely free.
You would be wise to do further reading on the issue of protecting yourself against malware. See my Mac Malware Guide.
Finally, note that the major printed Mac magazines have basically become shills for anyone who can pay them, since their business model of supplying a printed magazine that is a month outdated by the time it's mailed is beginning to fail in the face of always up-to-date online news sources. They were paid to review MacKeeper, and did so without any real scrutiny.
If you're interested in the opinions of people who have given it scrutiny, you should note that MacKeeper is currently the subject of a class-action lawsuit:
http://www.consumeraffairs.com/news/lawsuit-challenges-mackeepers-clean-computer -claims-012114.html