...don't use radar detector, it's totally forbidden and very dangerous to be kept with it.
And a US unit will most likely not even work over here anyway... it'll yelp at every automatic shop- and hotel door, but likely remain silent on the stationary speed-cams... different frequencies/systems plus the fact the EC speed-cams track you from behind, right
after having passed them...
(Only Germany uses small, mobile speed-trap units that clock and photograph you head on, as they have a kinda weird justice system in which the authorities need a photographic ID of the actual driver, and not only license plate/holder of the vehicle...)
Fix installed speed-cams are not so much of a concern for me, as their pretty visible... beyond that are there actually signs posted, "warning" that you're entering an enforced speed limit zone... a paradox though... ;-)
IIRC are there like 5 different camera designs used in France (the N4 is kinda loaded with them), so the unaware might not instantly identify them right away...
On dual-carriageways the cams are sometimes located on the shoulder of the oncoming lanes, but once you got accustomed to also look on the far left, you'll also spot those well in time...
(incidentally tripped one on my way to Paris this September, but still no
priority mail from the French Gendarmes... must have been a "banality" then (I usually keep my +<10kph margin), not worth pursuing it...)
So more of a "trouble" are unmarked police cars and/or manned ambushes, with their hand-held LIDAR guns... they clock you face on and are often ingeniously hidden...
But, those are active near the end of a quarterly, and mostly dormant the rest of the time... so... ;-)
-helmets : honestly, I don't think you will be arrest for a lack of stickers.
Doubt so too, besides that ATGATT has reflective patches woven in on strategic places (can't use flash photography on riders in gear, as those 3M threads overload every digital cam...)
As a conclusion, try to use twisty roads !
Concur totally...
There so many beautiful B-, C- and D-roads avail, that you won't like to ride on the boring nationals anyway...