The French tag & beacon always seemed a tad clunky to me. OK for cars, but the system for bikes is somewhat convoluted.....
https://www.saneftolling.co.uk/faq/#tag-use-faq-section
If I were to use this, I don't want to be queuing at toll booths to have my tag read manually, nor do I want to use a tag lane where overheight vehicles can pull in behind & corrupt my toll payment.
Sounds a bit negative I know - how do you find in in practice Wapping?