I did a change of address and 90 day report at Korat Immigration a few weeks ago. I didn’t need any forms as both officers (ladies) did it all for me in their computer system. The whole process took less than 30 minutes.
When I updated my new passport info a couple years ago (Bangkok Bank Siam Paragon), they didn't even tell me what they were doing until they were finished. They actually CLOSED my account and opened a new account with the new info.
I actually did use an agent when I was in Bangkok. I found it well worth the fee. I have seen some agents that claim they will “take care of” the bank issue, but I’ve stayed clear of someone offering what is obviously questionable.
I used Fast Track last week when returning from a trip to Hong Kong. Long lines at the regular immigration counters but Fast Track was NO wait. Also, my under 70 wife can use Fast Track because she is with me.
I had contacted them about a month ago for visa help.
There was something about them that gave me a bad feeling, so went with another agent who actually took me to immigration and I met the officers doing the visa processing.