I just recently bought some xaxim - a very non-ecological product, but I couldn't get Epiweb in Poland... I planted my U.campbelliana on it. It's a very SLOW grower, but since I keep it vertical it looks like it's growth got better. I kept it in a normal pot before. The red rectangles show the places where new leafs are emerging and the old ones too:
Looks like the species growing vertically are not doing well when kept in classic pots. I'll try the same method with U.asplundii.