I’ve been using my Monzo card for more than a month now, including while travelling on the tube and on buses. Not sure whether it’s just my card or not, but I’m experiencing a delay when tapping in and out. It typically goes something like this:
Oyster card - 0.5 seconds
Other contactless (Barclays, in my case) - 1 to 1.5 seconds
Monzon prepaid card - 2.5 to 3 seconds
I’m not sure if this is happening because the card is a prepaid one currently and it’s generally not a big deal, but sometimes it can get annoying in peak commuting times.