Reading the MOT regulations
The side repeater can be part of the front direction indicator if it has one of the following:
a wraparound lens marked either with an ‘E’ mark in a circle or an ‘e’ mark in a rectangle with a number 5 above it
an amber light coming through the front lens when viewed from 1m to the side of the rear bumper
I didn’t see a lens, so I guess you need an E-mark. But MOTers often don’t go around checking the e-marks. But you would still be breaking regulations, in a way a bit more obvious than US-spec sidelights being fitted.
I was told that the rear number plate that was on my old red Roadster and which I transferred to my blue Roadster, would be absolutely fine, not a word from the MOT tester, both in Northern Ireland (who are all civil servants) and in GB. And that was the case until the day I was pulled over in busy traffic in the middle of Watford, and served with a fine.
Sure, you might fit these. And they might pass an MOT, until the day they don’t. And they might not attract the attention of the Law until they do. Its clear these are unlawful, but you might get away with it.
These things seem mega expensive for what they are. In my opinion (only) they fail the taste test on a classic car.