Also if you follow the procedure above, you'd be using the same sealing O rings for 10 years.....
If you buy a cheap disposable oil filter you usually get both sealing rings for the oil filter cap (and the copper washer if you have an /m) included.
(not sure if every supplier adds those rings though but its something to watch out for)
Why is that important?
The outer sealing ring is obviously to stop leaks, but in the oil filter housing cap sits a pin (its an oil feed pipe) that plugs a hole that goes directly to the sump. This is constructed this way because you dont want to drain your oil filter (to the sump) every time you switch off your engine. That would mean that every time you would start your engine (with empty/drained oil filter) you would starve your engine of oil for the duration it takes for the oil pump to fill the oil filter cavety.
On the other side if you change your oil filter it would be nice if that cavety drains empty so that you dont have to fish your oilfilter out a fully filled bucket of old oil.
Thats why bmw (and many other brands like mercedes etc) use this setup. But in this setup its important that those inner seals are changed with the oil filter change (or at least once in a while) because you dont want to have them failing.
Here you can see its construction:
Trying to source those seals seperately (the dealer is probably the only place...) is probaby just as expensive as buying the £6 oil filter kit (Mann is indeed also my favorite filter brand, and Knecht is also good for oil filters)
I dont see an added bonus in using that steel oil filter. The paper oil filter element has no flow issues that I know of and if you use a decent brand at the recommended change intervals, I've never seen an oil filter collapse in these cars.