The black is just draggy, and the climb has absolutely no redeeming qualities at all. Deliverance is fun, and there’s a few odd little bits of descent that actually offer a challenge, but it’s mostly just not worth the effort.
Go do the innerleithen red – an actually interesting climb with enough techy bits to keep it challenging, and a descent that rewards you for the climbing effort. Then if you still fancy riding do the red at glentress, far more reward for your effort.