@Stuart ********
The only reason I wanted to use it is because immigration told me to come back tomorrow, the day my stamp expires.
I showed up 10:00 am with all my paperwork (I was impressed with myself). They told me I had all my paperwork but the queue was full and they're not processing anymore today. Effectively Pattaya immigration only does extension between 8:30 and 10:00.
I go to great lengths not to use Pattaya immigration office.
But, I think your correct that the system doesn't work, at least in my case, I did't try Bangkok.