We bought the 'suck it and see' towing mirrors after seeing a friend who had them. Whilst I appreciate concerns that they might 'un-suck' in transit, we've not had a problem over several weekends away and a return trip to France.
The best thing about them is, because they are attached to the mirror glass itself, when the driver (Mr H) wants to re-angle them, they simply adjust them on the electric controls rather than having the passenger (me) having to reach out of the car and respond to 'up a bit', 'too far', 'back a bit', 'down a bit' etc etc.
We bought them on Amazon, just make sure you get the flat and convex versions, one for each side of the car. I assume they're universal for all makes of car.