I know that feeling!Definitely go for the TAG. The only time I have had any concern, was when going through the toll that lets you drive at 30kph and worrying it hadn't picked up the signal, only for the barrier to rise at the last minute
I’m with Hutch as on one occasion we chose a RN but it had long stretches of two lane road. Sat following a long line of heavy goods vehicles and the never ending ups and downs of speed limits persuaded us to break off and rejoin the autoroute. It’s by far the best if you need to knock off the miles but the other routes can be very nice if you are doing a more leisurely journey.The Tag is great, the battery last for 5 years and they tell you when you need to replace the tag, Some folk like not to use the Peage routes because of the costs, I tried the side routes a couple of times, and after taking about 2 hours extra and using more fuel because of the village roundabouts, decided we would rather pay the toll fees.