When I first started in this forum, I was new to the world of actually practising martial arts-- now I'm about at a 16-year veteran status. I've trained in a multitude of arts from an array of gyms and dojos, and Kenpo-Karate is still one of my all-time favourites. Nothing compares to the efficiency of brutal kill/maim strikes to get out of a life/death fight as quickly as possible-- but I have since acquired a lot of much-needed skills from arts which Kenpo didn't provide. Contact sparring from Muay Thai, soft controls from Japanese JuJutsu, ground-game from Brazilian Jiu-jitsu, take-downs from Judo and American Wrestling (largely based on Greco-Roman) and punching from straight-up boxing and kick-boxing.
I mention all this, because what I'm trying to say is that to know whether or not the school is "good" depends on what you're trying to get out of it. You can't practise Kenpo full-speed with your friends, because everyone will get hurt. So you can't take away a lot of very useful aspects of martial training from this art alone, no matter how good the school is.
What I would look for in a good Kenpo school: attention to detail from your instructor and training partners. No half-assing a technique, because a slight variation in hand placement or strike location can mean the difference between a highly effective technique, and garbage that will get you hurt.
A good school should stay focused on the class, teach you as much as you can absorb in a single setting, have you repeat it until they're sure you're practising in the right way, and expect you to come back with that technique down. Then they teach you the next one(s).
Kenpo doesn't offer much grappling, and if it does, it's probably a more modern style and/or a mixed version of the art. That's not necessarily bad, but just make sure you understand what it is you're actually learning, so that you don't call it the wrong thing among particular people who you may wish to be positively viewed by, so that they'll take you seriously and either teach you or learn from you.