We used TWOV three times in the last two weeks at PVG and everything went smoothly.

I was worried using it back-to-back might be an issue but needn't have worried.

check-in staff varied... a couple of check-in agents read timatic and thought TWOV was 15 days (not 72 hours). others knew the rules. CX in HKG took the longest, entering in ticket numbers from a separate booking.

only one entry entailed a short (3 minute) delay... coming off a United flight where I don't think the check-in staff entered enough information for the Chinese authorities. in that case I was asked to go from the individual booth to the central booth and asked to fill out a separate from with my contact details in china and my hotel (which was the same as my in-bound card anyway).

for PVG at least they seem very comfortable with TWOV. my last entry the print-out was missing the airline designator before he flight number. immigration knew it was an air china flight and processed it no problems.

on all entries we told to join the regular immigration queue. only once did the 'special lane' also flash 'transit without visa'... but we were still asked to join the regular queue.