We were in Tenerife the last 2 weeks in September and spent many happy hours on La Tejita. The previous time we had tried it was at another time of year (April/May) and we weren't impressed as the weather wasn't great (overcast) and the wind made it worse. However we thought we would give it another go as we were staying closer this time (San Blas). The sun was hot and the breeze kept it comfortable so it was very pleasant and we have totally revised our opinion.
It is a huge beach and handy with the car park so close. There were a mix of naturists and textiles and, although the southern end (right as you look out to sea) was nearly all textile, you are free to walk anywhere along it if you wish. After the first visit I even walked to and from the car park naked, undressing and dressing by the car. Although I didn't see anyone else doing this, apart from my wife, nobody bothered.
There are 2 lots of sunbeds. The ones in the middle appeared to be all occupied by textiles but the ones to the far left seemed about 50:50 naturist:textile. On various parts of the beach people have constructed stone windbreaks and we were always able to find one of these by which to set down our picnic blanket.
There were 2 lifeguards on duty (in the middle and to the left) but no other facilities apart from 2 portaloos behind the beach at the Montana Roja end.
What a coincidence, I was on that beach myself today and it's exactly as you described it. It was my first visit after arriving in Tenerife yesterday, I'm sure it won't be my last as I plan to return again tomorrow. 8) 8)