My understanding of the Gussi box, is that it's in Class E (+tmz), but as the contents of it will be VFR, there is nothing to stop IFR traffic routing through it, as long as traffic information is provided. Personally, I would pass traffic info on the box itself, and if asked, or deemed necessary, vector traffic to miss the box.
I think the 'peculiarities' stem from the fact it's the first reserved area in 'controlled' airspace that isn't classes A-D, and the access rules therefore throw up some unusual scenarios.
Some of this stuff is also why IFR pilots are specifically told when they are entering/leaving class E.
HTH.