Well
@RT4038... I embraced the empirical approach of the OP, and did indeed have a check on my commute yesterday. For reference, the journeys were on service 9 from Brislington P&R to Temple Meads operated by Stagecoach using standard e400mmcs.
Journey in - 0756 ex Briz
The bus was already on the stand at the P&R and 30 passengers were already on board as the tracking indicates boarding began at 0748. There were 20 passengers in front of me, queuing. On average, each of those 20 fares took 3.5 seconds - it was about 70 seconds to load. Most fares were card payments with people getting £3.50 returns to town but some had Megariders on their phones as they didn't receive a physical ticket. It was all very quick indicating that many were regular (not daily except the Megarider) passengers. We left at 0756 on time and a mix of lighter traffic and extensive bus priority saw us arrive 1 min earlier at Temple Meads. Exiting was also straightforward though their were no people looking to board.
Observations: fewer mobile tickets reflecting the fact that it's cheaper to get a return if you don't have a four or five day commute. That may have slowed things slightly but there were no ENCTS passes either and it was quick.
Journey back - 1626 ex Temple Meads
I was outside Temple Meads for 1615 and casually waited and watched the various First buses trundling past to Broomhill, Stockwood, Bath etc. At 16:26, my 9 was 3 mins away. At 16:29, it was 2 mins away. It actually arrived at 16:35. Five people exited taking 17 seconds. 16 got on again with an average dwell time of 3.5 seconds but with the 17 second hinderance, it was 4.5 seconds per person.
17 seconds is an encumbrance but nothing in comparison with a) the fact it was 9 minutes late and had delayed in what had become almost standard rush hour traffic and b) it was a full standing load and I actually couldn't board!
Instead, I paid £3 to get an X39 to Bath Road and ran through torrential rain to my car! That was similarly easy for boarding except when a group of 13 yr olds went to get on and Sienna (or "Siennuurrrr!!!" as it was pronounced by her friends) was slow in getting her stuff together. Most people boarding were doing m-tickets or TOTO (as it is a First bus). It was actually a dual door machine and the exit doors did help at the Brislington village stop where there was some counter flow of passengers (though the TOTO validator was out of use). However, we did have to fight to reach that stop and up the top of Brislington and that delayed us more than anything.
So my experience and caveated with it's just two journeys (but I do it fairly often and it's broadly typical)... off bus ticketing is probably quicker but I saw no particular issue with the speed of the Vix machine in processing cards even with paper tickets being issued. Dwell times were not egregious. What really screwed things was the traffic. There are several pinchpoints on the A4 and just getting vehicles through the city centre would help no end, perhaps by re-routeing the 9 to head by Redcliffe Way rather than battling along Temple Way. The point is that when halving the dwell time saves seconds, a couple of mins at most. A badly parked car or poorly designed junction blows that out of the water!
