A 20mm tyre on a 21mm wide rim is asking fro trouble. The tyre should at the very least equal the rim's width. Normallly rim width + 1 mm.
That said, I never had any particular problem with Veloflex Corsa be that a 20 or 22mm one. They're light so they're bound to be pretty skinny. Don't expect the impossible and avois glass shards and other urban debris and all should be fine.
Pretty fast and comfy too. Especially so when outfitted with a decent latex inner tube.
Record is just too skinny for regular road use, it's a specialty tyre designed for time trialing.
would a 20mm tire on a 21 mm rim give you the same aero benefit of the wider aero rims that are all the rage
For starters wider rims aren't more areo (not when width is measured where it should be measured when we're talking rim width anyway) and a narrower tyre on a wider rim is about the least aero as can be.