For the money it's tough to beat. The typical daily driver type trickflow H/C/I car I tune runs high 12s low 13s. Start getting more drag race oriented with the car and low 12s and beyond are doable.
Valve guides do tend to wear over time, I was discussing this with one of the engine builders we use just the other day. I would not let this detract you from the kit, however. Be sure your pushrods are setup properly and it will live a long life.
Wes