Good questions, not sure what kind of improved level of security there is. Why do I need to show my ID if I passed a background check then passed a fingerprint check on site?
I can't speak to other airports, my business takes me to airports not serviced by clear.
Shoes and coats come off, no real difference to the screening process other than you feel like a VIP cutting the X-ray line. Certainly faster for the individual (at this time) but not sure about the system. I am not sure it was designed to speed up the system. I think it was designed to make it faster for those willing to pay, kind of like E470. I wonder when there are 20 or more clear passengers on line will they be have the personnel to take your stuff up to the front, etc? Not sure.