Flamestrike
Legend
I'm not clear on that. In character, do you get to ask your patron for a boon? Or does your patron grant whatever/whenever on their own schedule?
Because if you (the character) do get any influence, I think you'd definitely consider asking for things that you couldn't get any other way. Not saying you wouldn't ultimately go with your vanity...
But it's a very different proposition than just trying to do your patron's bidding and if they're sufficiently pleased then you get what you get.
Though now that I read closely, it says "In your studies of occult lore, you have unearthed eldritch invocations..." so maybe you can direct your studies, so to speak.
Mage armor is better than the light armor you could (uncomfortably) wear. It provides an AC of 13+ dex which is better (and less of a hassle putting on each day, and far more comfortable than) any light armor in the game.
Plus there are other advantages to having an at will mystical force field you can summon whenever you need it.
Plus; Warlock.