My experience: They will crack, generally only hairline but you need to be aware. They also stain if not sealed properly, which will need redoing to keep the floor durable. But yeah, they look great. Be aware that if you're looking to have one put down you'll need to lay a new concrete slab in the area with 75mm insulation (and usually underfloor heating). You'll need to allow 80-100mm for the polished concrete too.
The worktops, same advice really. Long-term it will probably pick up stains, but they can be more forgiving aesthetically than say marble if they stain.