They talk about it being more environmentally friendly, however how many of these ingredients that you growing, then cutting, and processing the hell out of them are you using. You "egg" is made from an acre of Soybeans, don't you feel good about yourself, with a good portion of it going to waste. While my Egg is from a chicken that has eaten 1 acre of feed and produced hundreds of eggs during its lifetime. And the chicken works as a rather efficient little factory of making eggs.
If you're going to argue that using pea protein instead of eggs is less environmentally friendly, you'll have to do better than just making up some numbers. The chicken seems rather inefficient since if all you want is the egg, doing things like growing, moving around, maintaining life, etc. all are inefficiencies in the plant to egg process.
On first glance, it would seem that it's more efficient to use the plant-based version. Hellman's Mayo is 8% eggs while Hampton Creek's mayo is under 2% pea protein. Even if the chicken was ultra-efficient and converted 1g of feed to 1g of eggs, you'd still have to show the that process from pea to pea protein was at least four times less efficient.
Given that one of their main points / goals is to be less expensive than using eggs, it seems unlikely that the plant-based version would be less efficient.