Comparing modern Cobra trailers the glass top is less expensive and
(subjective) looks better than the metal top. I would also expect the
glass top to be easier to repair in the event of minor damage. I have
no concern about UV penetration of the glass top. It is double
skinned.

The downside of the glass top is that the the finish does not seem to
last no matter how often it is polished and waxed. The dealer that
sold me my ship suggested it would be cheaper to repaint the top in 5
years that to have paid for the metal top. We'll see.

If buying a used trailer you should look for a problem common to both
types of top. The base of the top is a special aluminium (there I
said it) extrusion that carries the retainers for the wing spar
fittings. If the top is closed with the wing fittings not fully
forward the retainer hits the fittings and the side rail extrusions can
be badly damaged. I have seen several trailers with this problem,
including one that was delivered that way from the (sailplane) factory.

Andy (GY)