The biggest downside with Powervision (our version), from an Admin point of view, is that the banned IPs are not listed numerically. This is non-changeable, and makes it hard to locate IPs that would be better banned by use of a wildcard.
This forum just places the latest IP ban at the top, and so on. So you may have bots that all use the range 255.255.255.20*, but you won't spot it. So you'll end up banning 9 IPs, instead of just one. Which is really tiresome.
As for security, bots seem to be able to bypass the system, if they want to - but it is much less that what we had with phpBB.
k:
You just need a good Mod crew, and a nice Dustbin to place all the bot spam, so that you can ban them. Don't just delete such a post, as then the bot will just post again later.