Proxypass does seem to be a bit better than most of the others, which are
strictly naive IP counters. It doesn't do quite the same analysis as Strongbox 2.0
and Strongbox 3.0, currently in beta, is a lot more sophisticated, but at least
Proxypass does more than just count IPs per day. The monthly expense is an issue,
and being an Apache module implies several siginificant drawbacks compared to Strongbox -
it may not work with a lot of shared hosting accounts, it can't be as easily moved to a
new server, etc. Personally, I'd prefer to design the system so as to minimize processing
overhead and keep the processing on the web server rather than constantly sending data
back and forth with their server, but I understand that design decision since they charge
a monthly fee. It's hard to charge a monthly fee once you hand over the full software
and that's one reason Strongbox doesn't cost $50 / month. There would be no way to
actually collect the $50 since the system doesn't rely on an external server.

Anyway, if Strongbox didn't exist I might well choose Proxypass for a busy site where
it was worth the $50 / month fee to have something that does a bit more than just count
IPs, but Strongbox does some pretty smart analysis that noone else can touch right now
and with the new stuff in Strongbox 3.0, including a basic biometric test, there's nothing
else out there that can so effectively stop shared passwords. We've gone from fairly
accurately indentifying a specific computer to actually including indentification markers
for the human being sitting at the keyboard so we have an indication if two people using
the same computer access the site or if the same person accesses the site from more
than one computer and I don't expect Proxypass or anyone else to be able to match that
any time soon.