Is the bar sizing right, or would it be a bit too small? Don't know about the size needed for greys, sorry. It doesn't have wire diameter either so it's hard to tell if it's more suitable for an IRN type bird rather than a stronger beak. Smaller bar spaces tend to go hand in hand with smaller wire diameters.
In terms of the top, I personally don't like the ones that open. I do think they're unnecessarily dangerous, I wasn't aware of the reason you've put but it does makes sense, although they're generally quite heavy to open so it would be quite an unlikely accident. I dislike them because when they're open, if they're not securely held open (and let's be honest with birdy beaks around not much stays secure for long!) they can fall closed and hurt, trap or scare a bird. With care the dangers can be minimised, but my personal preference is cages with play stands on top.