Never ordered a PPS before, but the first advantage that come to mind in terms of the diecast version are the additional articulation and extra accessories like the Tony Stark HS and the diorama base, which give you so much more posing options. I personally love the additional heft of the diecast figures (I think they weigh twice as much as their plastic counterparts according to Budget Stark's video) and have come to associate it, subjectively, with the quality associated with the figure. It is something that one could only truly appreciate if you hold the figure with your own two hands.
However, those advantages are moot if you have a thing for statues and have no concern with creating your own pose for the figure. Also, visually, the PPS and Diecast version look the same; you can't tell the difference between diecast and plastic till you actually pick the figure up in your hands. Some might even argue that the PPS version might resemble the on-screen version better because of the lack of articulation, and the fact that plastic Iron Man figs tend to have sharper details than their diecast counterparts.
Personally, if given the choice to only have 1 Iron Man figure in my collection, I would pick diecast over PPS any day. To me, if I were to ever only possess one piece of something that I really like, I would want that to be the best option available (if it fits into the budget of course). Speaking about the price aspect, yes the diecast figure costs almost twice as much as the PPS version, but you would also have twice as long to save up for it if you choose to do so; I think the PPS version is out Q4 2016 while the diecast version is only released Q3 2017. Still, even at $190, the PPS doesn't come cheap because just adding $20 or so on top of that gives you the chance to buy a "full" MMS version instead (probably why I never found the PPS version to be of great value).
I think the Mark 46 is unique in the sense that it might be the only time we see an Iron Man figure with 28 light up points; none of the 45 before it had it, and it's possible that those that come after it might not have it either. I haven't seen the armor in action on-screen yet, but this design is such a perfect mix of old and new that it's officially overtaken the Mark 6 as my most favorite Iron Man armor
Thanks for sharing the video. 
Spoiler: 
