Standard stainless fasteners are softer than standard steel, and pathetic compared to high tensile steel. They are fine for 6mm case and cover fasteners, carb stuff, almost everywhere. Not for places where thy carry high load - the larger case bolts that hold the crank bearings together primarily.
Durability is hard to quantify. They will last a whole lot longer than steel if you live near an ocean or ride on salted winter roads. The softer metal will round off hex heads or spin a phillips driver much easier than steel. That's more an issue for fumble-thumbs using wrong sized or adjustable wrenches though, not us
The hex head stuff is better than phillips, if you use the right size tool and seat it fully you shouldn't have problems.
Use anti-seize for stainless/aluminum and you won't have seizing or corrosion. Without it the stainless fasteners can eat the threads in the alloy cases.
