I have bought 2 x tyredog systems........
First one worked really well.
Till I went on an outback trip.............
Admittedly we drove some pretty serious stuff and it was tough going, but I wrecked the external sensors.
Then ones on the camper just copped too many stones on them and got destroyed and I wrecked one on the car.............
That negative said, I have had a really positive experience with them. I only put them on when I go on a trip, I don't use them for every day.
I think the best bit is being able to monitor the camper tyres from the car.
Don't expect an external sensor to cop serious off road business and you should be fine.
In hindsight, I should have fitted the internal sensors, but also in hindsight I'm a billionaire............
Live and learn, but I reckon they are worth the money.
Cheers
Brian