That was the point - the question was "would you use pattern parts ?", as in use parts not coming from the car manufacturer. As we (probably) all know, a huge proportion of any car is bought in parts - and buying the OEM part without the car manufacturer mark up is usually a huge saving. And then there are other manufacturers who might not be the OEM, but are of the same standard.
And then, there are others where ... you have to be a bit more cautious, hence the ACME reference ? In the Land Rover fraternity, there is a parts supplier who supply many parts for older vehicles, but have a bit of a reputation for ... "variable quality". It's tricky with them since some of the parts they sell are actually OEM parts.
Back to electrical ...
Talking about the issue of only using an approved assembly (ref a few posts above). What if a CU came with some fixing screws and the MIs said it could only be fixed in place using the supplied fixings. Would that mean that you'd have to scrap it and go buy another one if you dropped one of the screws and couldn't find it ? Or would you simply substitute an equivalent against the wording of the MIs ? And what if the fixings provided just weren't suitable ?
I know this is taking things a bit far, but if you think about it, the screws used to fix the thing (assuming suitable) will have as much effect on performance of individual breakers and the whole assembly as a correctly sized piece of copper cable (e.g. RCD-neutral bar link).