I had dual SUs on my MG 1100. Man, what a PITA they were. Because of the east-west engine orientation, the carbs were between engine and firewall and nearly impossible to get at. The were so small (13/16 choke, I think!) that they were too close together to get one of those balancer gadgets in.
They have died in the US because of emission rules. They're very high emitters of unburned hydrocarbons because of the way they handle transients.
The worst example I have encountered was the Japanese copy (Keihin?) installed in a twin-cerb set-up on a Datsun 260Z my daughter had. It was a lastgasp at trying to get this type of carb to meet the emission rules of the time. There was a double-skinned inlet manifold with coolant piped through it, then each carb had a coolant heated base around the jet that the needle operates in.
They do give enhanced performance, but the amount of messing about you have to do isn't worth it, IMO.