Not a factor because the lens isn't "interfacing" with your camera on any level; there's no electronic or mechanical connection. You're simply recording the image that the lens is projecting on the adapter GG, like recording a movie off a theatre screen.
There are many. Cinema lenses can be much much sharper than cheap SLR lenses. Also their iris ring rotates continuously instead of in increments. Their focus ring is already gear AND the ring rotates the opposite way from SLR lenses. Downsize is that they can be incredibly expensive, easily surpassing the cost of the adapter.
