Looks very much like Nikko Blue, which is a very robust and remarkedly hardy variety that will often rebloom. Semiremontant.

That said, a lot of big blue mopheads look very much alike :-)

The leaves are too glossy and the plant looks too compact to be a Nikko... Its either an older free-flowering variety or some other recent reblooming introduction. You might want to ask the person how long they've had it, etc. I got an unidentified variety in a 4" pot from a funeral arrangement and it overwintered better than most everything else, now it has 4 deep blue blooms way deeper than ES, Nikko or anything. Could be Brestenburg which I hear doesn't need terminal bud hardiness to bloom.

That looks like a forever and ever because of the dark glossy leaves and how tight it is. Lowes is the best place to find one in my area (central pa)