It won't stop 100% bots, if it did NCSOFT would use it :)
It's just another layer of defence. The best way to fight boters is to monitor players activities.
l2JGuard can be heavy on the CPU and throw some false positives, but for the price is very good. I wish it would create a server side log of all intercepted bots etc. It shows some info in the GS Console but does not create a log for them.
Still, I would recomend it purely for the quality to price ratio.