I’ve used local bearing shops before and the bearings have always been superb. Usually a bit cheaper than the ‘proper ones’. Nice and convenient too. They usually have some friendly blokes in who look like they’re stuck in the 80s.
If it’s a faff to get them in and out then I’d play it safe and use the ‘proper one’ from whoever makes your frame… unless they’re lusciously more expensive.
You can usually find cheap bearings on ebay/online which in many cases I suspect are the same as the ones that I’ve bought from the local bearing shop. It’s just not something I’ve wanted to take a risk with. I don’t want to spend a couple of hours carefully fitting them, only to find they’re rubbish.
I would add that I suspect a lot of people jump straight into thinking they need to replace their frame bearings when they possibly don’t. If you keep the pivot bolts preloaded correctly, they occasionally work loose, and periodically pop the bearing cover off and add a generous helping of fresh grease they should last a long time. If you ride on the bike when the pivot bolts loose or the grease inside has long since vanished then you will put them into an early grave.