On the other hand.... I made my own rear calipers fit (135i calipers) and everybody was screaming dont do it, only big companies should do brakes etc etc, you will get a dangerous car...
Well... needless to say it performs flawlessly. I mean on a fairly comparative car using the rear calipers (as they were ment to).....
And now a few years later you see that the aftermarket has finally caught up and yes they now also can supply rear brackets etc to make 135i calipers fit for z4/z4m.....finally only 3 years too late.
So I see this project from daemonblitz (using F series performance brakes) the same way. He's just the aftermarket sector ahead
This set is by the looks of it also substantially cheaper than a front/rear set from one of the aftermarket manufacturers. Which is also important (if money wasn't a subject we'd all be driving around with $20k carbon brembo GT sets
)
And of course if you have the technical skill to fabricate brackets or adapt brake shoes or brake disks etc (whatever it needs to make this kit fit), you also have the clarity of mind that for the first testdrives you do that on an empty road and you do some max. brake test to see if the abs kicks in and to see that you dont have lockup at the rear (so that the brake balance is right).
That goes without saying. That is not something you have to explain to somebody who has hands on engineering skills. (that is something you should do every time you do work on your brakes
)
Whether you need it or not is a different question but that goes for every bbk. But I suspect that the 4 piston calipers are lighter than the stock steel ones, or house a larger pad. That is mostly the case with bbk's, they're either lighter or you get more friction material. Bigger disks are obviously heavier (both already have an inner aluminium hat).