Edit: Whoops, didn't notice I was double posting.
For a regular sniper (sniper rifle) this isn't worth that much - he has his back to the wall and is close to a sentry, he doesn't need defence. But! The other update; the bow and arrow, fits this weapon perfectly. He's now moving forward together with his team, and as he is scoping, he's eaten alive by his natural enemy - the spy.
Think about it - the sniper will be now leaving his places of safety, making him incredibly vulnerable. Not only that, his weapon still has a charge time, and requires some steady aiming, meaning you won't be able to watch your back.
And thus, the razorback. You won't have the same trouble againt spies, as you're now moving - and far closer to your team. Using the revolver is no longer as much of an option for the spy, and it's at least a far bigger danger. It might even cause the spy to go kill that spinning heavy rather than the sniper.
You could say that this seems a bit overpowered, but it isn't really. The razorback causes you to move slower, thus being an easier target for everyone else. If a scout gets past the front-line, you'll have some immense trouble.
In conclusion: The razorback is completely useless for the regular (old) sniper. For the new - bow and arrow - sniper, however, it removes the spy threat to a far lower level.
That seems to me to be the most plausible explanation. It's the same as the pyro; what is the Axtinguisher worth without the flaregun? The FAN makes up for the sandman's loss of the second jump, and the Razorback takes away the danger of spies, that you get due to the Bow and Arrow.
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.
