Well, you can probably guess what I think.
Pros.
Real power cannot be achieved without airflow.
Permanent.
Works even better when accompanied with forced induction.
Not as expensive as you would think.
Can be tailored to a specific type of driving/racing.
Cons.
Doesn't work well without cams and attention needs to be paid to other V/E enhancing items, i.e., intake, exhaust, fuel management.
Car is down while heads are at the shop. This could take some time.
What will keep the prices down is max'ing out the heads with the stock valvetrain. Which has been my goal.
Big-time gains can be made with increased valve size. Especially on the exhausts. Very expensive endeavour.