Very growly and slightly low-mid-focused sound, absolutely fantastic. They sound great on my Warwick Thumb 6. The string tension also feels a bit lower and I find the strings are much more comfortable for finger style playing than steels/nickels at same gauge sizes.
I've previously purchased Ernie Ball Cobalts for my 4-string bass and they corroded heavily in just a couple of weeks of playing at home (and my fingers are even not that particularly sweaty). I was afraid it would be the case with these too, but so far I haven't had any problems. Had them on for nearly a year.