Dave Liquorice wrote
Rod Speed wrote

12V halogens are at least twice as efficient as mains halogens.

Sure, but you have to allow for the lousy efficiency that
the transformer produces too when used in a house.

Except that gert lumps of iron wrapped in copper aren't that comon
any longer. The "transformers" are small SMPS's, less problems with
people swapping out bulbs with different ratings than what the system
was designed for or problems when a bulb has blown and isn't quickly
replaced.

And more problems with them failing.