As you already know, RX-77D armor comes with Fix Figuration 0028 RX-77-2 Guncannon - its definitely worth getting two of this release as they are both fine figures. The only bad thing is that you are left with a ton of armor as you can see in the final shots.
I think this could be the first Fix Figuration that comes with etching decals for RX-77-2 - it even comes with extra chest armor and foot just for the etching. I suppose there are going to be some ultra maniacs out there which end up getting a few of these just so that they can have 108, 109 and 203.
RX-77D
I think I over done it with the exposure for this round and there's a blob on the lens too - I must have had a late night the day before or had something in my eye like a shard of glass or rusty nail.
Anyway you can read up more on the RX-77D at MAHQ.
