The M50 tolling arrangements are daft!
I've missed the 8pm deadline a couple of times, and even though I want to pay the charges I can't do it until they issue a notice in the post, which last time was three weeks later ... and even though I missed two tolls on the same day I am still waiting for a notice on the second. Why can't I pay overdue tolls as soon as I want? -- the information must exist to process them!
There is no way I will ever be opening any of their account options. I've heard half a dozen first hand stories of people being charged for journeys they didn't take. The latest one, on calling the call centre, was told "oh that was a mis-read"... which means they are able to pull up the original photo and correctly read the plate where the computer couldn't.
For the privilege of being told this, you have to call their lo-call number (which is up to 30c/minute from a mobile), and if you DID have an account with them, you would simply be debited without you ever being any the wiser. There must be SOME cases of particular cars being regularly misread in the same way time and again ... you know, that bit of dirt that turn a 6 into an 8 or whatever.
I wouldn't trust them as far as I could kick them.