I use Marshall's organic extra, which is the same sort of thing, dried manure. It is expensive but a little goes along way, a couple of handfuls per square yard, and a sack lasts me several years. (Just looked it up on their website and there is a good offer on at the moment).
I am also a fan of rock dust having lived near the Seer Centre when they were developing and testing it and seen their results. In those days you could get large sack for £5 via a local quarry but since the big players got a hold of it, it too is now quite expensive, but again a little goes a long way.