Yep, that thar plastiky thing be an o-fishul dork disk. I always take them off. I just make sure my rear derailleur always stays inadjustment such that it does not run off the top of the big cog and into the spokes. <-- not too hard to do with a decent derailleur.

You're right about the chainguard on the Shogun, it's not too bad. If it were mine, it'd be taken off but as these things go, it isn't too bad at all.