I think perhaps it is if you take it as a learning experience, and don't lead them on to believe that you think they're the one. Be upfront about it, so you don't get labelled a heartbreaker afterwards. (Then again, if you are upfront about it, you take the risk they'll leave you.)
Why bother? Just have fun with the situation but don't get caught up & don't waste ur time. Best advice I ever got is don't get tied into a relationship u aren't 100% sure u want, and don't make a relationship outta sthg that isn't meant to be, it's a waste of everyone's time, you could be productive elsewhere in another area of ur life ... or even with someone else! lol.
Eventually you'll get bored of it. I call these "convenience relationships" because you're getting what you want- the dining, wining and knocking. bow chicka wow wow!