I didn't have a 3D printer and I certainly didn't want to spend 2X for an "OEM" designed mirror which typically are smaller. Noticing that the mirror stalk and housing was plastic, and that the wire that is capped by the torx screw is slotted through a very narrow opening, I decided to widen...
Indeed, but price is an important factor. The product you mentioned from Amazon is cheap and will work perfectly with a DC-DC step down buck converter, direct interface to the mirror port and no wacky wire routing. Companies like Hansshow are selling their units for +$400 to be purpose-built...
Having installed head units and cameras in other cars, with fuse taps or directly to battery, I believe your statement needs clarification on power draw. Based on several 4k/2.5k rear view products on Amazon, they utilize USB-C connectors and come with the cigarette lighter adapter for power...