Here is my experience. I am married to a Thai so I could have an extension based on marriage but I opted for retirement. I entered on a tourist visa then obtained my non-o in Thailand. I put 800,000 in the bank and applied for and received my retirement extension. Retirement is less paperwork so in my opinion less work. I then started bringing in 65,000 baht per month so that I would have 12 transfers for my next extension. At the time there were no requirements to keep the 800,000 in the bank for a certain amount of time. We used the money to buy some property. I still use monthly transfers because there is no requirement for me to keep money in my bank account.
For my annual extension it takes a few hours to assemble the paperwork and then about 20 minutes at immigration since I am able to make an appointment.