yep I paid 6000thb the first two times before I just did it myself. In fairness I guess it did save me the trip to Pattaya from BKK. But after the first two, I just used it as an excuse for a road trip and some seafood by the beach.
Some of the comments here seem to be commenting on generalities.
I've done the 60 day covid extension, and I went 1 week 'too early' before my previous (covid extension) expired, and they wouldn't give me the stamp, and I had to go back the week after to get the stamp. That's when the visa extension starts from.
you buy it the day before, you go through immigration so if they ask for it, you're covered, then you cancel it. You can literally buy anything at any price, because you'll be cancelling it.