Good question, and I'll give my reasoning, to get input from others. Not because I'm sure my reasoning was sound.
1) I live where YouTube (and others) are blocked, so I download like a fiend on my monthly visits to Thailand. Sometimes, I'm out and about for hours (with my cell phone) and my computer is still downloading the queue of files when I get back to the hotel.
2) My cell phone SIM (AIS) has limits on data. It's been awhile, but I think it throttles back the speed if I exceed the limits, which is easy to do when downloading like a fiend.
3) For 1200 baht ($35USD), I didn't mind ponying up to try one out. The TRUE SIM was the biggest part of the expense (2990 baht) and the nice guy who set me up at Fortune Town said they had the best plan for unlimited data. (Had I just stuck the TRUE SIM in my smartphone, that would have meant yet another new phone number)
4) In the past, I have had data plans that don't allow hotspotting. I think those were mostly in the USA, but my brain leaks. Does anyone know if any Thailand carriers "discourage" hotspotting?
Edit: And one other observation... It was so nice to watch a guy who knows what he's doing open the box, insert the SIM, and activate it for me on the TRUE system. I walked out with a fully functional system. That's worth money to me.