Keep an eye on them. As they age they may start shedding rubber dust and other stuff. We had them at work and no amount of sweeping would get the dirt off them (this is in a bindery) and even if they looked clean if you had to get on your hands and knees on them to work under the folder you got a thick layer of dirt on your clothes. I preferred the bare floor.
I have seen a variety that had a hard layer laminated to the top side that stayed considerably cleaner. Ever run into those before?