We went on a Saturday evening having turned up on a Friday 45 mins before the thermal baths were closing and being led to believe this was not enough time. In hind sight this would have been enough time for the thermal baths. The baths overall are a good Budapest experience. I wouldn’t describe them as relaxing as they were very busy in the early evening. There isn’t much instruction on the best way around but that’s part of the fun! A tip is to start in the small 28 degree centigrade corner pool diagonally opposite where you enter the baths if coming straight from communal changing area and work your way around to next two higher temperature corner pools followed by main centre pool then finally the hot 42 degree corner pool.
We bought a ticket that included all areas as we wanted to try the rooftop pool which was part of the wellness area. The rooftop pool was a bit of a zoo but nevertheless there were great views from the comfort of what was effectively a warm communal bath!
As to cleanliness expect good local authority pool type cleanliness. It is a busy thermal bath with lots of people so naturally not sparkling clean but really not too bad and that said from someone who is a bit of clean-freak! Definitely take flip flops and a towel (both available to buy otherwise).
The whole experience might not be to everyone’s taste given how busy it was but we enjoyed it!