I like the idea of the shield, but there's a problem to it: The revolver.
The spy revolver deals almost 70 damage at close range (as in, backstab range). Two revolver shots take hardly no time, and the sniper won't have a real chance of fighting back (going out of the scope and into a battle within less than a second would be rather hard).
Personally, I already use the pistol over the knife on most snipers. Many snipers pin themselves in a corner, so rather than hope the sidestab is on the back half, rather than the front half, why not just shoot him twice? The only real advantage I see from this, is that 2 snipers won't be backstabbed in a row as easily. Single snipers don't get a lot, but if you're two at the same point, this will help you. Oh and if the sniper is close to a sentry. A lv 3 sentry will kill him (provided he is not directly behind it) before he can kill the sniper.
Ubers are not invincible. Push them over a ledge, they're dead. Train kills them. That's just completely wrong - enviornmental deaths can kill them.
When I write Fact: in one part of the post, and opinion: (or a similar word), it's not because I can then say "my opinion can't be wrong". It is to inform what part is pure facts, and which part I try to draw a conclusion in.
