I went through a series of spring changes trying to set the bike up on the cheap.
I first did a spring change to Hyperpro front and rear. I still have that spring on the rear and as the miles add up, it seems to get better. At least it does not spike as often, which is probably caused by losing its compression ability. I plan to keep it until the rebound goes away.
The first aftermarket cartridge replacement was made by Bitubo. A self contained gas charged unit. Only adjustable for preload. Beside that, the major issue is the difficulty in recharging it after repairs or valve changing. I did not like the valving so resprung it with an Ohlins. .55kg.
It all works fairly well as long as you realize it is not really a 500# dirt bike.
I have come to realize doing it on the cheap will add up.
Unless BMW did something between my pre order bike and when everyone else got them, there should be no question which end is better.