Just got back from a 2 week trip in Turkey/Thailand/Japan. Ended up using Airalo for all 3 countries - there were slightly cheaper options available, but theirs were good enough to go with the simplicity of using them for all.

Turkey took quite some time to activate. I had been on the ground for over an hour before it suddenly started working. Once it was working, it worked fine. Roaming provider, but I'm not sure who it was roaming to.

Thailand was my first non-roaming eSIM - it was sold as being through dtac (one of the major Thai providers), and sure enough it was directly through them, with no need to enable roaming to use it. In hindsight, I could have bought this eSIM directly from the dtac website for slightly cheaper (literally about 30 cents cheaper!) but would probably go with Airalo next time again just for the convenience.

Japan was through Singtel (roaming onto Softbank) and mostly worked fine, although I did randomly lose coverage several times in areas of Tokyo where I'm sure Softbank would have had coverage. A few minutes later it would start working again. When it was working I didn't have any performance problems as reported by Majuki above, however I really wasn't pushing it enough to know.