Im using the trial (30 days) since Im not completely satisfied of the mac firewall application, and cannot spend days and days learning how to manage the unix firewall - even noobproof is a bit too complicate for an average user like me. So far, after teaching net barrier how to react, I've encountered no problems at all: no crash, no undesired services block, no slowdown in my old macmini working, no interference with my heavy internet and intranet work.I had to install it to prevent further problems (hacking tried on my mac , I think through Upnp open ports- now Upnp is shut down) and I have to say Im fairly satisfied.
Net Barrier is a bit expensive (when it will be discounted again with a MacUpdate promo?) but I think, since Mac hardware and software is becoming more and more popular, there are some security risks, and people working on the computer several hours cant sacrifice hours just to try to prevent hackers to ruin their work.
So I think I'll buy the license, since, at least with this last updated version, I've not experienced any of the troubles other users had apparently, and finally I saved lot of time and I feel (and I am) safer in my work environment.