I found XS hostel on a site listing hostels on Isla Mujeres. There were no reviews, just a website with prices.
I emailed them in advance, in English (my spanish is barely passable), and asked for a reservation for the first two nights of my stay. The website lists dormitory rooms, and "private rooms" as well.
I asked for two nights of private stay, and received an email response, in english, confirming my reservations.
When I arrived, the owners were extremely, but spoke really no english. My fault, but it made for a funny check in process.
The "private" room was really just one of the dorm rooms, with 4 bunks, but all to myself. It was $40 a night, which is somewhat average for the island. I like my privacy so I was happy.
The room was clean, the bathroom worked, and there are 4 "safes" in each room to store your things. The quality of the safes are not the best, plywood cabinets, basically, but enough to keep honest people honest.
I stayed for two nights and the location is great. Literally 2-3 blocks from Playa Norte, and directly next to Hidalgo, so all of the places to eat and shop are within a 5 minute walk at most.
If I were traveling alone, I would probably stay elsewhere as you can find single hotel rooms with AC for the same price in the same area.
If I were traveling with a group of friends, or didn't mind sharing space with strangers, I would stay here without hesitation. Give them a shot, especially if your spanish is up to par. Mine wasn't, but they were extremely friendly and accommodating just the same. Overall, a very pleasant experience.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.