Another factor that may not be readily apparent, that applies to the idea of a early days recreational OW diver going SM, is that it will (modestly) extend your dive times on a two tank trip, even more so if your buddy is also in SM.
To clarify:
If you do proper gas management, on a 30m dive in a single, you will need somewhere around 80-100 bar in an AL80 to get two working divers up safely with a reasonable ascent rate and a safety stop. That means that you will end up with somewhere around 70 bar or so left in your tank unusable on the first dive. After 2 dives, you have 2 "empty" tanks containing around 140 -150 bar of gas that goes back to the shop instead of being converted to bottom time.
With a SM pair of divers, you only need to ensure that you have enough in either tank to bring you up safely. In practice, this means that the gas for the second dive acts as reserve for the first dive, so a little careful planning means you end up with 2 tanks of around 40 bar left after the dives. That 800 litres difference, for me, means around 15 min extra bottom time. Not a big deal, sure, but that can be quite valuable depending on the site and cost of getting there.
The caveat of course is that if there is a problem on the first dive, you may not be able to get a second dive in but thats the cost of doing business.