Manufactured cam vs machined cam

i think what your friend now has is a "regrind" cam, they are not as good as a cam thats ground from a "fresh" blank like a Spoon, Crower, Skunk2 etc cam...those are EXACT grinds, and are tuned exactly to each application depending on how "mild" or "wild" you want the cam to be

If your N/A, go with a bought cam, if your building a turbo monster, get a cam fresh ground to what you need. With N/A 99% of thee time you dont need to have custom lift and dur. but with a built motor AND turbo, youll want to have a custom cam and a custom ECU isnt a bad idea either, that way youll have your maps set to your cam and internals.

Might have factors with what kind of metal they are made of.

this is true, with a regrind, go with a stock shaft. For a AFM cam, stainless or better, never go with the old school iron cam or the aluminum cams, but will crack or worse under high heat and RPM.

Regrind cams accelerate wear on the rocker!
Personnaly, I prefer aftermarket cam because they surpass hardness and quality test! And it depend on your need(type1-2-3)
Type 1 will pass emission test-good for daily driver
Type 2 dont pass emission!-still good for daily driver-good power
Type 3 big power with other mod-not so good idle-emission...haha

regrind cost less but you will never have the type 2 with a regrind cam....