[Gelbster]

History(SEARCH !) is a wonderful resource.
There are plenty of much cheaper "correct" size bearings than you quoted .Try $2 on FleaBay.
The results of fitting them have been mixed.
One memorable disaster involved a good quality replacement from a decent vendor -Boca Bearing fitted by a prolific Forum member .
Boca Bearing , to their credit advised against it. He fitted it anyway with many postings about the money saved.Car was quickly sold to another Forum member.IMSB failure was almost immediate. Of course most such cases do not get published.
The cumulative wisdom is that yes, you can use a generic bearing but you'd better know what you are doing. Start with a discussion of ABEC and seal material.There is more geekish detail - and that is just the steel ,deep groove bearings. If you include ceramic-hybrids and rollers the discussion would be a magnum opus.
DOF is not new. But not with grease ! And anyway it has been somewhat discredited in cumulative wisdom because splash+seal removal or using a plain bearing is better.
So maybe the source documents you used in all that reading you did were old?
And anyway there are other upgrades to do at the same time that come in the kit so we have an apples/oranges problem with your price comparison.
There is a reason Pelican sell a kit and not just a cheapo generic bearing for the IMSB replacement. The above hints at just some of those reasons. First ,do no harm....