It can also be used on MTB, but we don't promote our saddles at all as a MTB saddle, because any MTB rider drops the bike sooner or later, and it will land on the saddle, which isn't designed to take such impacts.
For the seatpost - yes we will put a weight limit, mostly because it is designed for a specific weight to get the best properties in terms of comfort. It isn't the same if the rider is 60kg or 100kg, so mainly we'll put a limit because of that. In case of a bigger rider the layup could be too flexy and in those case we would need to customize it. But we are so busy that we didn't managed yet to put in production new products, but we work on that.
Otherwise some more photos from our workshop, working on the padded saddles:
Some Lukna saddles in matte and gloss:
And a photo from a weekend ride, in Slovenian hills, I guess our UK friends would feel great in that part of Slovenia