I got a DTAC eSIM at the airport over a year ago and have been using it ever since. I chose DTAC because its counter happened to have the shortest line on the day I happened to arrive.

The DTAC app has an "Order & Activate eSIM" with a variety of options. I have no reason to use that so I don't know whether it's possible to complete the steps outside of Thailand.

I have not measured the speed but it feels at least as fast as what I'm used to at home.

Yes I can tether.