After trying this plugin since it came out, I've had to pull it several times after major, server wide lag. Unfortunately I'm hearing other people complaining of the same. Great idea, just doesn't work.

Does anyone know if it can be applied to a specific zone or group setting to limit the number of buildings it is trying to protect (ie, minimize lag?)

I have put in the effort to rewrite this plugin from the ground up with performance in mind as of v2.0.0. While it will still have an impact, it is a substaintail improvement over previous versions. I have even provided a preset configuration available in the documentation section geared to save server resources wherever possible. I recommend giving it a try and seeing if its more feasible for you now!