Thanks Tim, I'm happy to hear that our demo sites are useful. Another demo site that I often use is the Moodle sandbox demo to check if a reported bug can be reproduced.
Regarding the QA testing site, do you ever use it in between QA testing cycles, and would you find it helpful to have two testing sites in future - one on 3.11 and one on 4.0? If so, please comment on MDLSITE-6231.