Ditto on not really needing the electric shield. I rarely, if ever, used mine. I found it more of a hindrance and discomfort because of the way the plug wire fastens to the chin strap. And, the wire seemed to always get bound up in the pivot point of the shield. It might be useful if you were to encounter wet snow or rain that were freezing to the shield, but for fogging issues (which in my experience with the BV2S are minimal at worst) I found the electric shield to be unneeded.
Also agree that they do run small, so it's best to try it on before buying. They're also quite warm so you may find that you don't need a balaclava or facemask to keep warm. I wear a thin balaclava only in extremely cold temps, like 10 or 15 degrees or less.
One last thing....the early models used a silicone type sealant between the two panes of the shield, which apparently didn't allow it to "breathe"; so when the air in between the two panes expanded, it would cause the shield material to bubble (which is permanent). Later models incorporated a foam seal between the two panes that allowed for air expansion without damage to the shield. Make sure you're not getting an early version, or else you will inevitably end up replacing the shield.