I haven't had time to look at Darktable - I did look at it a year to two years ago, and concluded that it wasn't ready yet.
I'll try and take another look this evening/weekend.
I'm not quite sure how to say this next bit without sounding like I'm spoiling for a fight, so I'll just say it:
I won't use it just because it's free. (Either as in speech or beer.)
I've never been fussed about paying for quality software - which I think Bibble is. I would rather use free (as in speech) software, but some kinds of software or support just won't happen without money being involved. If the price is reasonable, and the product/service is decent, then I'm happy. I'm not going to get ideological about the hobby (photography) that I enjoy.
Darktable will have to be better than Bibble to make me switch, not merely adequate for use... So whilst I'll evaluate it with an open mind, I have to admit I'd be surprised if I decide to switch...