They have their place but they also have their drawbacks, consume more resources and are more likely to suffer a system performance hit. If there is a problem with the main interface or integration of the AVs then you don't have even one. So for me I prefer the multi-application approach to security.
I wasn't too impressed with the time I tried hitmanpro as on-demand, whilst I didn't expect it to find anything, all it did find were false positives and I reported both, over a week later they weren't resolved. So I don't know if that is a) identifying which element detected it and b) them having to contact multiple companies to correct the FP.
If it is lavasoft's adaware, I feel this is a much depreciated anti-spyware.
