I've been there twice!
Discovered it on a trip to NM with a troop of Boy Scouts - then came back twice with family to dive & tourist.
This was all high summer - when it's GREAT to jump in and cool for a while - so I spent a fair bit of time working on holding neutral at 5-10 ft while enjoying being surrounded with new, but tiny, fish! - My teenagers got real bored, real quick!
Otherwise - Dee & Bill are right - it's about 2/3 acre of spring, max depth ~25 feet, and most of it set aside for swimmers with concrete flooring. A few larger catfish, bass and a turtle or 2 - lots of the tiny pupfish and other spring natives. - Very pleasant, but not really inspiring.
I really like it as a tourist jumping off spot. - Dive in the morning - then off to McDonald Observatory, Ft. Davis, and whatever other local things to do - then back for a late afternoon dive or just hang by their nice cabins watching the life in the canals connected to the spring.
OR - you can finsh your DiveMaster class!
Cheers