The cardboard mod is not a shield. Cardboard doesn't shield anything. The cardboard mod does absolutely nothing for most people. The ONLY thing the cardboard mod does is prevent the copper shield from electrically shorting or screwing with exposed solder on the bottom of the GPS. That's why it is called the cardboard isolation mod, not the cardboard shield mod. Unfortunately, that bit of information is lacking from most posts on this mod lately.
The 3DR v2 shield is an improved shield that replaces the copper shield. It is engineered RF absorbing material, that specifically absorbs RF in the band that interferes with the GPS. It is orders of magnitude better than the crappy copper shield. It is also not conductive like the copper shield, so the cardboard isolation is no longer needed. I struggled horribly with getting and keeping a GPS lock before the v2 shield. It was BAD. And often unusable. With the v2 shield, it's a whole new drone.
That said, I agree the mRo GPS is still a worthwhile purchase. The things that make the original GPS suck are still there. The new shield just makes it less of a problem.