I'd call shenanigans. For one, that's more like a permanent power, and it should be bought like that. We had a similar discussion a short while back.
Second, remember what is said about wards time and time again in the novels. They need something to be built upon, preferably a threshold. The stronger the threshold you have to work with, the more you can attach to it. But what are you going to attach this personal shield to? Your ward at home? Ok, the ward stays at home. It is a cool description of how it works, but it stays there. Put it on a bracelet? Wait, there is a rule for that: enchanted items.
So no, I would not say it is legal. And even if the argument can be made, that it is by the book, I would still not allow this in any game I ran. You either handwave all the preparation steps, in which case it is highly overpowered, or you play a few sessions about the character getting his "I'm invincible" shield on, which does not really seem to me like an interesting thing to do, and even if it is, it should be reflected as a power of some sort or another. If it is something special, like a heat shield because he needs to get to the ground of a live volcano, that's a different story.