I can only talk about my office but I had to use an agent during covid when I did not have access to funds as I did not expect to get stuck on Thailand. I had problems getting COR got hassle when doing 90 day report and generally given the run about over many issues I faced. They did not like me having a stamp from outside the province. They flatly refused to transfer my stamp into my new pass port so I had to fly to Bangkok. Agents have their place and some provide a very good service but you are on safer ground if you do it yourself and you can spend the fee on something more pleasant.
5 years. 4 years now and again and the last year once a month. Never had a problem . I dont need transfers in seconds. A couple of days or less suits me fine.
Ignore anyone who tells you to use an agent. It is a waste of money and does not save you much inconvenience. It could also cause you a number of problems in the future so it is much better to do it yourself as John Stanners has also explained.