Theoretically an all glass laminate free of synthetic cloths (like polyester and kevlar) will shatter rather than bend when it reaches the breaking point. This means THEORETICALLY that if you wrap the boat horribly you have a better chance of breaking free of it. Glass is a stiffer cloth than polyester but has a lower sheer strength. An all glass deck will be stiffer than a glass/poly deck but will crack easier because it does not bend (similar to carbon only not as strong)
The downside it that it may only break part way and trap you worse. For example the deck could crack free next to the seam but the cockpit rim not break leaving you more screwed. Also on the downside it could break sooner than a glass/poly laminate again leaving you more screwed. It is also not uncommon for a fiber to "fail" but not "sheer". In laymen's terms this means crack and bend but not break. What this means is that even though the fibers are e glass they are still pretty strong and will hold together even though most are broken apart.
All glass cockpit and leg areas are referred to as "breakaway cockpits" by the upper yough old schoolers who invented the idea. Way back when the "Ark" was the hot boat, the company Phoenix went as far as using chop strand mat cloth (non woven thick heavy stiff but brittle cloth) in the cockpit area.
There is no agreement on which is better and I do not recommend one over the other. I do not know of anyone who has ever actually used the properties of the boat to help extract them from a pin. The principals have never been scientifically tested. Even if they were, fiberglass work is not far removed from alchemy and it is impossible to consistently duplicate the humidity, temperature, and dozens of other factors that are present when building a boat that could affect the properties of the matrix.
No matter what material the boat is made of you can forget the idea that you can be cut free of a wrapped boat. On dry land with a jig saw it takes several minutes and at least one fresh blade to cut through any major area of a boat.
It is a personal decision. Ask around with some people in the know and then make your own decision. Most boats today are glass/poly laminated and the builder will not even mention glass leg areas for "liability" reasons. It is just an option I have available to those who want it and are educated on the advantages and disadvantages of it. Obviously the best thing to do is not take your boat anywhere that pinning could be an issue.
ONLY TAKE YOUR BOAT IN SAFE DEEP FAMILIAR WATERS
There is no charge to utilize the all glass leg option.