I suppose it depends on how difficult it is to change the bulbs.

On my last trip to France I bought a set of bulbs that will dip to the right so I can swap the bulbs on the ferry and dispense with the beam deflectors.

If your car uses the H4 bulb, they are quite cheap - less than 6 euros a pair.

I was under the assumption that a bulb was the same the world over if its a H4 in the uk its the same in France,the dipping is to do with the headlight housing and reflector not the bulb.

I live in France with two Uk RHD vehicles that we brought with us. The oldest one, an 05 Mitsubishi L200 pick-up truck had its first CT (french mot) at 4 years old last Feb, Reluctant to buy two new headlamp units, I reset both headlamps on dipped beam so that they are aligned to the right ,result- passed CT no problem. I personally wouldn't bother with the "beam benders" they just don't seem to do anything.