The MX-170 was not the most reliable bit of kit on the market, I seem to remember two or three people who got them fitted and had no end of trouble with them.
No doubt there would have been one to two lucky people who had reliable units but this would have been very much against the Run of play.
Those who paid more and replaced their KX170 with a KX155 ( or KX165 ) would have found themselfs financially well ahead of those who went for the MX170 despite the much higher inital cost.
History is likely to repeat its self and fitting the much more expensive GTN650 will pay dividends in the future.