I'm a U.S. citizen and I first stumbled on the "no more income affidavits" bulletin when I happened to browse to the U.S. Embassy & Consulate website in March. Then I searched around and came upon the rule changes that went along with that (from thaivisa.com). I had already enrolled in STEP but never heard anything from that side. And it would have been nice to hear about any immigration rule changes via a form letter sent via Thailand Post. I'm pretty sure Immigration has multiple copies of my current address on file. But of course that would only happen in a Southeast Asian fantasy world. So I then started playing the new game as soon as I could in April by making monthly international fund transfers to my Thai bank account.
Anyway, I could see using an agent as a lazy Plan B (for this transition period) if IO didn't show leniency in November with my less than 12 monthly international funds transfers -- assuming the agent could get the job done before my current extension ran out. Otherwise, yes, it'd be a cold day in hell before I'd waste 23,000 THB on an agent to do something so easy. I will show income deposited in a U.S. bank account (from self-printed unofficial statements) for the remaining months (they won't even want to look at that) to show my sincere best effort to follow the rules even for the transition period, and I will think positive, smile, be clean, not wear rags, and... get leniency.