Was an Clear member from the old program and SFO is my home airport so Pre or not, I'm extremely happy Clear is back. I'm a UA 1K and the Elite security lines are a joke. Many times it's slower than the normal line with everybody and their brother having elite status via credit card, etc.
I used Clear for the first time at SFO Int'l G gates a couple of weeks ago and it was the same as before, through Clear check and security in less than 5 minutes even with the full body scan.
I believe with Pre you have to wait in line to get your boarding pass scanned, so Clear is definitely faster in that respect since you immediately bypass any/all lines and the TSA agent/scanner and go directly to the detector. (I have enrolled with Pre as well since I already have Global Entry so will be ready for that once UA implements it later this year.)
As a frequent biz traveler anything that cuts my wait time at the airport is worth the cost...