I would not pay full price for it, getting it for a sales price, yes. Then I find it worth having on my system. It's mainly a preference thing. Others may prefer EEK or NPE, both of which are free and really good at finding things, maybe too good in NPE's case (fp).
I've been using the free version for years as a second-opinion scanner. By default, it runs a quick scan daily and a full scan monthly. I've seen a few false-positives on new/obscure software, but overall I think it's a valuable tool.
I have been using Hitmanpro for years, sometimes I use the free version, sometimes the paid version. Currently I'm using the paid version on my main machine My other 2 machines, I use the free version.