Lots of options for the "S" psionic monsters:
--I am going to pass on the Shedu, since I have done so many other "Guardian/Watcher" monsters of good alignment. The Shedu and the Lamassu are basically the same beast, mythologically speaking, btw.
--The Solar? Statting out an arch-angel.... wow, ok, that's cool.... I probably won't be using these things, since I am dispensing with the "all-powerful extra-planar gods" thing.... I could see using them as stars in the sky. Literal stars, I mean... like in Voyage of the Dawn Treader, a star in human form.
--Slaad are pretty cool. They are basically just frog-demons by another name. I could see introducing one or two of them in that context.
The Su-Monster offers a nice psionic addition to the average "non-celestial/non-demonic" game. They can be used as nice wilderness or dungeon encounter for example.
As far as I can tell, they are unique in being a race of psionic animals. Basically, they are a race of psionic baboons! Come on, you gotta admit, that is pretty cool!
The one thing I don't like in their 1e MM description is the idea that they are "immune to psionic attacks". I say fie to that. If they can attack with psionics, they can also be attacked by psionics. I am not willing to put them in the same class as the Phoenix, as being somehow immune. The Phoenix, sure, he is the apex monster, literally immortal, I'll give him a pass. But a psionic baboon being immune, come on...
Anyway, the Su-Monsters like to hang from their tails and attack in ambush. Makes sense to me. First, deliver a mind attack, and when the victims is sitting there trying to figure out what the heck just happened, drop down on it and tear it to shreds with your four claws! Sounds kinda like an Intellect Devourer, really.
I can see a troop of these blighters carving out a niche in a dark, evil forest... Even the goblins and orcs avoid the area... In AZ adventure, they live mainly up in the Chuska Mountains, which is Ground Zero for the psionic monsters of AZ, nearby the Githzerai fortresses in Monument Valley, the Githyanki lairs of Canyon de Chelly, and the Mind Flayer infestation of Chaco Canyon....
They have a latent "6th sense" for detecting psionic power usage, which as always, includes psionic-like spells... Thus, these things could quickly become your stalkers if you use your powers anywhere in their domain... For that reason, they would also be used underground as guardian type monsters.
--Perhaps taking on one of these things would be a nice "initiation ritual" for a young Psionic Warrior...
--The brains of these things are also highly valued for use as magic ingredients for spells and magic items that emulate psionic powers.... Thus, there would be a definite market for the capture of Su-monsters, which is always a nice plot hook.
attacks: 4 claws and bite (1-4 and 2-8)
Psionic ability: 120
attacks: d6: 1-2 Psychic Crush, 3-4 Psionic Blast, 5-6 Mind Thrust
defences: Thought Shield
For the effects of these attacks on non-psionics, see:
Psionic Blast http://oldschoolpsionics.blogspot.com/2010/11/psionic-attacks-on-non-psionics-psionic.html