Is there optical distortion with the polycarbonate plastic?
Yes. We looked into this during development. Polycarbonate with no optical distortion when viewed through at the angle the windshield is used at would make the product cost prohibitive. The prototype in Z-Lab has some slight distortion, but once in the driver's seat and focusing past the windshield on the track it is forgotten.
I understand polycarbonate/plexiglass scratches easy. How does this perform?
It is plastic and not glass so it will scratch easy in comparison. We looked into abrasion resistant coatings from the polycarbonate manufacturer because of this, but the windshields have to be formed because the coating is not as flexible as the polycarbonate itself and will crack. Again, this becomes cost prohibitive to solve. Z-Lab has run the same windshield for a year now and while it does have some fine scratches on the surface, it is like the distortion. Look past it. Liberal use of Rain-X for Plastic aerosol cleaner and fresh microfiber cleaning clothes lightly used on the polycarbonate will extend it's lifetime. Replacement polycarbonate windshields are available.
Does it fog up?
This depends on how you vent the car. Fogging happens when there is a large enough temperature differential from the outside to the inside of the polycarbonate water condences on one side or the other. Z-Lab has no vents on top of the dash, so whatever is happening outside is basically the same as inside. We have driven Z-Lab in the rain on a cold morning and using Rain-X for Plastic on both sides of the polycarbonate helped keep it from fogging up.
Does it leak?
It is not necessarily a sealed installation, meaning the polycarbonate is bolted to the aluminum frame and there is no gasket. This is for off-road use only, so sitting around in the rain for extended periods of time is not expected. Even so, the only place it leaks on the prototype is around the fastener heads and not a lot. The rest of the edges are covered in trim to keep water out of the original sealed glass installation. If you want it water tight, it could be sealed around the edges and under the fastener heads with RTV. It just makes it more difficult to replace the polycarbonate.
How is driving without windshield wipers?
As expected, if you have to drive in the rain on the track you should have enough speed Rain-X will stream the water away. Z-Lab has run twice so far with the windshield installed in the rain/wet track conditions. The only time it was unnerving to not have windshield wipers was travelling at 140+ through water running across the braking zone with a GT3 rooster tail covering the windshield right in front of you. Otherwise, the Rain-X does it's job. Just re-appply frequently.