You can definitely recover another Trezor with the same backed up passphrase and both units will have the same seed and key set. Basically the restored backup would be identical to the original.
I wasn't aware you could do that, but still you don't want two devices to share the same seed and key set. If one Trezor gets stolen then the other is also unsafe.
True. If your Trezor is stolen, you have to assume that the thief will eventually guess your PIN. So you have to move your funds as fast as you can.
But if you don't have a trusted computer (and therefore don't want to risk a local software wallet), you could use a "cloned" Trezor to move the funds temporarily to another wallet (maybe Coinbase if you have no other options). At that point, it wouldn't matter what the thief does because the funds associated with the keys in the device he stole would be worthless.
Then you could initialize the backup Trezor from scratch with a brand new, uncompromised seed, then transfer from your temporary wallet back to the "new" Trezor. Since it has a different seed and key set, it's just as secure as a brand new Trezor.
I agree that this scenario is a bit of a stretch. In my case, I've assumed that if my Trezor is stolen, I'll use Electrum on my laptop to quickly recover the seed, then send the Bitcoin to my backup Trezor, which I would initialize with a new seed. I'm on Macintosh and am security conscious, so I think the brief possibility of exposure of possibly compromised keys is worth the speed to move the coins.
But other people on more vulnerable operating systems (not to start an OS war or anything) might want to go the the other route for safety sake. In this scenario, having a cloned Trezor just for the ability to safely move the coins out of the hands of an attacker isn't necessarily a bad idea.