I booked the spa and afternoon tea package for myself and a friend as a treat. It was pricy, but completely worth it.
We went early on a Saturday morning and had the pool/sauna/jacuzzi/steam room all to ourselves from 9am to about 10.30am. The massage and facial were great, and Leo the beauty therapist was brilliant. The treatments did last as long as advertised, and we weren't under pressure to buy anything afterwards. It was lovely sitting in the relaxation room after the massage, though a lot of other spa users were trying to get into the room and rattling the door which was the only thing that spoiled the ambience. (It's a locked room for people who have just had treatments - you can't get in if you're just using the pool or gym)
I would recommend going early in the morning like we did so it's quieter - we arrived around 9am and had our treatments at 11am, then afternoon tea at 1.30pm. By the time we were getting ready for our treatments the place was filling up, and it was so much more relaxing having the place to ourselves. Afternoon tea was great too - the quantities were unlimited and the quality really high.