It says that you can't counterspell to dispel sustained spells on another plane but counterspelling as spell defense should work just fine. The fluff even mentions that it's accomplished by disrupting the mana around the target.. You still don't actually have anything to do with your actions though unless someone comes to hang out with you in the Astral. And things that your team just walk through like Wards and Mana Barriers are suddenly a big problem.
Popping into the astral at times is very handy, but doing the entire run that way seems like a huge waste.
