They're Dean Markley's alright!

ULTRA smooth to the touch, and the light-grey silk sound exactly like em.
I do have a set on my p-bass, and a 5-string set on my Ibanez BTB, and they are definitely one of my favorite flatwound strings!
alot of people don't like them because they find these strings to go "dead quickly," but like you said, these strings are thumpy enough to have a great upright bass tone.
hope that helps!