I too just recently signed up for it. I don't transit IAH much so my datapoints will not help you. LAX/SFO thus far have been very efficient and I've only beat the pre-check line by a couple of people since there rarely is a queue. I'm waiting for LAS this week.
Heads up, sign up for a Delta account. Clear drops to $99 for a General Member, less if you have status(originally $179). Even beats my Alumni Association offering $139.