I know this is awkward but if everything doesn't slowdown, the more you have, the better. Moreover, there are still features not available in the free software. By evaluating it, I know i'll make a better decision when I'll have to opt for a product. And easy comes, easy goes. I unistalled some moments ago the Advanced WindowsCare Pro. The giveaway turned out to be a scam without database updates. In the near future the CounterSpy trial will reach the limit. After that, goes the WLOC. Then, I'll load others.
The key feature of the new software is they find again old trojans and keylogers that remained in te recyclers and in the restore references.
While my system keeps its agility and stability, I'll keep testing it with whatever new is developed. I do have a junk PC with which a test first the software, by charging against the cracking code community - these are really mean guys. I do have friends who test antivirus against their emule and kazoo overnight delivery. After this testing, we learnt there isn't a restfull security software alone.
So, the more and better you can have and the more your system can load, the better.