about 4600€ for the prop but I think plus mounting plus charger unit?
It seems as expensive as the ones in the market already. Probably it has to be expensive but even so it is much better than a generator and in boats that don't use a lot of power and sail a lot it will be perfect.
The way I sail and with top batteries (AGM), a big alternator and a regulator I really don't need it. 45m a day of engine work is enough to keep all systems working and I do that motoring a bit when I leave the anchorage and motoring a bit while searching for a place to anchor and of course there are days where there is not any wind and you have to motor longer.
I don't think that the cost of that system is justifiable for coastal cruising where a maximized electrical charging system will cost about the same price and is more reliable and have other advantages.
Regarding Oceanic sailing, transats or more extensive navigation in a fast boat, it is the right tool and allows all systems working without never turning the engine on. While on shorter daily legs on coastal cruising, typically 5/9 hours you can steer for considerable time and not use the auto-pilot. when you sail non stop 24 hours the auto pilot is used more and the consumption is higher, besides those 45m to charge the batteries regards day sailing, at night the consumption is bigger.
Anyway, most cruisers I know pass much more time on anchorage then while sailing, most passing several days on each anchorage or port. For those the system will not work at all.
If I decide to cross the Atlantic I will mount one of those systems that on fast boats that can sail most of the time are pretty much the thing to have, unless you want to motor without any need to do so.
Heavier cruising boats, that typically have a much bigger tankage, need a lot more wind to make a decent speed and on a crossing they would use a lot more the engine so that system does not make much sense. If you have the tankage and a slower boat, unless someone wants to circumnavigate, the cost of the extra diesel used on one or two transats to charge the batteries will be a lot less than the cost of that system.