The biggest con is that the amount of games on the SA market is A LOT less. A pro is that some of the games are cheaper on the SA market.
Currently, my GF's account is UK and mine is SA and it works well for us. Capcom just had a sale and all the games I wanted was cheaper on the SA account and I got them from the SA account. However, three of the games I wanted, is not available on the SA market (RE Code Veronica, RE 4 and Super Street Fighter 2 HD Remake) and I got them on the UK market.
So, my suggestion is: Keep your main account UK and create a free SA silver account. Best of both worlds.