I've been to quite a few spas in the city and this one is definitely my favourite! I love the co-ed lounge space, it's nice and bright because of the skylight. There are day beds for you to just hang out for a few hours before or after your treatment. In the women's change room there's a separate room with about 6 adjustable beds if you want to nap or just to have some peace and quiet. There's a good selection of snacks and Sloane tea - if you're hungry you can order from their menu as well!
As for massages, I've only had good experiences here - they're very professional massage therapists and extremely courteous. I love how they provide you with tips and advice at the end of the session to help ease pain or tension. They even demonstrate the stretches you will need to do - I haven't seen this elsewhere yet. The rooms are really nice, I did a couples treatment once and went in the cloud 9 suite which is a large and beautiful space!
It gets kind of busy on weekends, usually all the day beds are taken and the bathrooms get a bit more crowded - which can be annoying when you want to get your things and people are just standing around in there looking at their phones. Other than that, try to book during the weekdays. (I came around noon on a Tuesday and I had the place all to myself!)