I previously posted about visa run following 90 day stay on non imm O visa. I only want to stay for additional 30 days, therefore will passport entry stamp at Malay or Myanmar border suffice or do I need to get SETV? British passport holder.

Crossing the border will get you a stay of 30 days.

A visa exempt entry will get you 30 days. However, you will not be able to do this at most border crossings to Myanmar, and should probably avoid Sadao on the Malaysia border.

The crossing to Myanmar at Ranong allows crossings for a new visa exempt entry. All other do not allow them.