If a part is OEM this means that it has been certified and is used by the manufacturer (e. G. Jaguar). The only difference between the OEM part and the manufacturer part is the box. Sometimes even the box will be the same. For example, Bosch is an OEM manufacturer of ECUs for Porsche and Jaguar. Jaguar buys ECUs from Bosch to fit to their cars. You can either buy direct from Jaguar/Porsche or go to Bosch or a Bosch supplier. They are exactly the same parts and have exactly the same part number. But one will be cheaper. Jaguar/Porsche will have their markup and may be a more convenient place to buy from. But it is exactly the same part.
Do not mistake OEM for a pattern or 3rd party manufacturer part. These may or may not be good enough for your car. But an OEM part has been specifically approved by the manufacturer.
I would be satisfied using OEM parts to repair my car over Jaguar parts. After all, I don't own a Jaguar and have never purchased parts from them before. The OEM parts for my car are priced better and they do the job. I wouldn't be satisfied paying more for Jaguar parts as that isn't very practical.
I would not be satisfied using OEM rather than Jaguar parts to repair your engine. While OEM parts are cheaper in the short term, they do not last nearly as long as the original parts. I do think it would be good to use OEM parts because they would not last as long.
Jaguar parts are something that I know and trust to serve my needs and keep me safe. OEM parts might always be physically designed to work with my engine, but in my experience, Jaguar parts not only fit, they operate smoothly and do not cause any warning lights to go off.
I would not be satisfied using OEM parts rather than Jaguar parts to repair an engine. I suppose the joke is on me however, because given my current state of poverty it is unlikely I would ever be able to actually buy a Jaguar. At the same time, I'm pretty sure, even if I did have the money, I still wouldn't buy a Jaguar because it would seem this brand is solely made for the purpose of impressing other people. I don't pay for such things, because I don't care.
I would not be satisfied as a consumer to use OEM rather than Jaguar parts to repair an engine. I do not think that I would buy a Jaguar in the first place, but if I did, I would not want to use EOM parts rather than authentic Jaguar parts. I think that is only natural for car enthusiasts.