Ever watch a grown man fight a table in the rain? Buddy of mine got a cheap aluminum roll top one and the whole thing folded up on him while he was setting down a dutch oven, beans everywhere. He ended up just using the tailgate after that, which honestly seems like the move unless you really need the counter space.

Oh man, read canned air spits on sensors too.

That $650 unit from the big box store is probably a 6 year tank, and the one the plumber had on his truck was likely a 10 or 12 year. You didn't just save $750 on labor, you may have bought yourself a shorter clock. Also, same day Sunday work in Albuquerque means the guy is probably paying a helper double, pulling a permit you don't know about, and hauling your old tank to the dump, which costs money too. Check your city code before you call it done, because a lot of places want a permit and inspection on a water heater swap, and if you ever sell the house that can bite you. The part nobody brings up is the warranty, since a self install usually kills the labor coverage and sometimes the tank coverage too if they ask for a receipt from a licensed plumber. I'd have done the same thing you did, but I'd have priced a 10 year tank at the store first to see if the gap was really $750.