Hi Frank,
The 240V MR16 versions put roughly half as much light in the centre of the beam as the 12V alternatives, so they are considerably less efficient. However lifetime is still 2500 hours. The main problem is the big filament which leads to imprecise beam control and low colour temperature.
In fact, the 12V market is one which has almost completely now been taken by cheap Chinese sources. Thus a 50W lamp which used to deliver 900 lumens and last 5000 hours, now typically delivers 700 lumens and lasts 1000 hours. But the price is halved and that seems to be all the customers care about today.
240V version are still mainly produced by the Western manufacturers so the quality isn't actually all that much worse than the common Chinese 12V alternatives in reality. But give it another year and I expect all European production of 230V halogen reflector lamps will cease. Customers have no real interest in lamp quality today and within another year or two the Chinese are expected to completely take this market also.
James