There is a 3-4 weeks under consideration even if you use an agent. So passport stay with them or with immigration on a pile somewhere waiting for their turn to get the yearly extension. It's been like this forever.
This group is own by the biggest agency in Thailand (Thai Visa Centre), you can ask them... they will answer the same thing. You are confused between using vs not-using an agent. You can read my response to Jim Stuart above.
What you are describing is without the use of an agent, but if you use an agent, the passport stay with them because after a few weeks u get stamped for the full year. So yes, the under consideration still apply, but you don't need to travel twice. A lot of people use agents from other provinces, as some provinces don't have reliable agent. Just because you do not understand what agent do, or don't use them, doesn't mean it's dodgy. Maybe ask question instead of making judgment :). The owner of this group is an agent himself.
It's standard procedure for "under consideration". Most likely he is getting a year long extension so he need to wait 3-4 weeks to get his passport back.
I don't think it's any different than getting a tourist visa, except that you need to do this visa in your home country, or pre-covid in Perth Australia you could do it too. So you can't go to Cambodia and get the STV.