I consider AIOs a huge waste of money. What are you paying for? A little section in the back to hide equipment? Is that worth hundreds markup over a Petco $ per gallon aquarium? Not IMO. I'd rather put that money towards livestock. You can buy a piece of black or blue acrylic for cheap and slot it with a dremel, install with silicone and bam, you've got an AIO.
yeah I thought about that too. but what I consider you are paying for in the low iron glass and build quality.
one could get a aquamax 22 low iron standard tank for $200 and still need to filter it some how. so price wise you in the same boat.
but yes if you did not want/need build quality/rimless/low iran the petco 20L is a nice tank.
and I might just use the one I have too...