Re: Ernie Ball Cobalt good for jazz??
As a jazz player, strings are strings. In the end it's mostly about feel, and most of that feel comes from how the string feels when bent (tight, loose, string tension etc). With less emphasis on bending, most strings honestly feel the same to me, unless they are coated or are a completely different shape such as flatwounds. Roll down the tone knob and a lot of the strings start sounding the same to me too.
I haven't used them personally, but the one minor detail that would put me off them is that Ernie Ball advertises them as very loud strings, not a trait I would normally look for in a string in a jazz setting. I don't believe it would be much of a difference, as I've used a whole bunch of different random strings on my jazz box, and the differences were minute no matter what. I'd say its worth a shot.