These are for sale via the TwoSixties website and other sources but think I would rather pay a premium from a more reliable source like the TwoSixties.
They replace the standard 70mm throttle body and supposed to give 10+ horsepower improvement, more if used in conjunction with other mods like a K&N filter.
Not sure I’d notice the 10 extra bhp on the already 260bhp but if it gives an improved mpg then it maybe worth considering making the mod. When I asked on Facebook I was told that based on rolling road tests not to expect more than a 4bhp gain with this mod.
MG ZT info mods and maintenance 