It's a nice collection, but the problem with STOS is that you really have to upgrade to 2.6 for STE compatibility.
Postage to the UK would also be expensive. I think many people used the version that came on ST Format Cover Disk and upgraded to 2.6 with the free upgrade. Was it free? I can't remember!
The manual is nice to have but available online. I don't think anybody used STOS 3D. DMLs 3D routines were far better.
I had a Master Sound cartridge and I think that came with STOS replay routines so there wasn't any need for that either.
The Sprites 600 has some nice examples but people didn't reuse the sprites as people would say, "Oh, that came from Sprites 600".
The version of STOS I used came with the Discovery Pack and the manual has a blue cover. I still have the manual for that!
I did get the compiler for £5.69 including postage with the manual a couple of years ago on eBay just so it looks nice on my shelf.
Still got, still working: Atari 4Mb STe, 520STFM, 2.5Mb STF.
Hardware: Cumana CSA 354, Ultimate Ripper, Blitz Turbo, Synchro Express II (US and UK Versions).