I like the idea of one of these Tag thinghies too but despite having read countless posts on here about them I am still totally flummoxed as to how they work, how much they charge, how they know I'm on a bike etc etc etc.
I'm going to wait until Wapping does another of his World Famous Wanders & try to tag along on that so I can watch the voodoo in action .
Couldn't be simpler....
Go to...
https://www.saneftolling.co.uk/
open an account, buy a tag etc
Have tag on front of bike, in tankbag...or even stick tag holder on screen,
drive through barriers, which go up, even the 30kph ones,
bill lands in sanef ac, money goes from whichever a/c you have linked to it,
invariably gets correct rate, but they promise to correct it if wrong.
by the way....'tag' along...I see what you did...
Have a look at the sanef site.