I haven't used the telepeage doofer, but from memory the lanes reserved for this purpose have a 2 metre height restriction, so I'm not sure how much benefit it woud be in terms of a speedy pass-through. I'm sure someone will be along shortly with experience.
So, if you have to use the normal lane why not just use a credit/bank card? It's very quick, no PIN, and removes the need for loads of cash!
Sid
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