Yeah Friendly readygrass is totally different to spillers (friendship estates) readigrass so it would be interesting to see a nutrition comparison of the two.
Mine absolutely love the friendly stuff, especially little Santa who I struggle to get to eat any other kind of hay. Calcium aside (and hopefully someone can look at a spillers readigrass and see what that says for calcium) it is still relatively high protein/lower fibre than standard hay so I wouldn't feed it exclusively - watch out for excess caecatrophs etc.