If my memory is correct, the reason people have cracked their windscreens when fitting wind deflectors. Is because of the extra long fixing screws supplied with the kit , these are used to attach the pivot brackets to the windscreen frame and must be cut to size - otherwise when tightening , the end of the screw comes into contact with the edge of the glass and the tightening pressure results in the screen cracking .
Personally I wouldn’t venture far without them , I find they cut down the wind(chill in winter) considerably & prevent the radio being drowned by wind noise . If you use the side screens constantly then there is no need for them.
