All the rigs of that type I have seen keep the boom and the clew slides back and forth along it..
Not sure how well a 'Wing Sail' will perform with the limited scope of a mono's main sheet traveler.
On a Wharram cat no problems.

I'd not seen a 'behind the mast furler' rig previously Boatman while I believe his logic was ease of mainsail deployment as his wife (who he generally sailed with) was also quite elderly. I didn't see it in action on any sea trial, and though it does seem sensible in some respects it does appear to be a heavy boat circa 21 ton fully laden to have such a rig?