I used it all the time (for goldsource) before the big updates to Blender 3-4(?) years ago. There's a thread somewhere here on TWHL by the developer and they had plenty of video tutorials on their site to get you started. Iirc, back then when i still had a max license, most known level designers in the CS GO community were using it in one way or another.
https://dev.wallworm.com/topic/72/goldsrc.html