Hi OP,
From the fuzzy picture, it looks like the right hand dial _might_ vary the radiator temperature (do they get hotter with it fully up and colder with it fully down? It will probably take half an hour or so to see the difference). Or does that dial vary the temperature of the hot water in your taps?
If it varies the radiator temperature, try turning it down. The radiators will take longer to heat your rooms, but they might still be up to the job of keeping them warm once they are warm. Basically, you should only need to turn the radiators up more when it gets colder outside.
I wouldn't worry too much about radiator 'efficiency'. All a radiator is is a device for taking heat out of water and transferring it to the room. If a radiator is better at doing this, the boiler just needs to supply it with more heat. All it means is that a more effcient radiator can be physically smaller to do the same job. Provided your radiators get evenly hot, I would imagine all is well.