First, the IFD-440 is a touch screen, which is really nice. For instance you see a frequency you touch it and it's loaded. It also allows for you to use the rotating dials, so you have that in turbulence, but the rotating dials have different logic than the Garmin, so they actually make sense to me. The logic of the rotating dials in the 430 change depending on which screen you are on. This was probably my biggest beef with the 430: it seemed like I had to think about how to use it all the time, instead of being able to use it as a tool. The IFD seems to just get out of your way, and help you do what you need to do, rather than adding cognitive load, the way the 430 did for me.
Another major difference is that the IFD-440 has built in wireless communication with for eflight, which is fantastic for synchronizing flight plans bi-directionally. so I can just enter a flight plan into foreflight before I get to the plane, hit a few buttons when I'm in the cockpit, and the flight plan is loaded in the IFD as well as foreflight for redundancy.
I also like the iPad app for the IFD, because it allows you vastly more real estate screenwise without a massive investment. In other words, the app allows you to control things like frequency switching, flight planning, or switching transponder settings, acting as if my IFD-440 had a 10-in secondary screen.
But probably my favorite feature, which sounds silly, but saves me a bunch of time, is the fact that it preloads frequencies as I move through my flight plan, automatically. I guess it turns out that I spent a lot of time while doing flight planning or in the cockpit looking for frequencies as I proceeded through my flights, and with the IFD I find that I really don't do that anymore, because the next frequency I need seems to always be popping up based on the IFD looking in my flight plan and/or my GPS location.
Last, but not least, there are a bunch of configurable display blocks, which have really useful information in them.
In addition to what's listed here, I really like:
-Geofill: as you are loading fixes it knows where you are and almost always selects exactly what you want after typing the first or second value
-Having the approach fix crossing altitudes displayed on the map
-Entering airways without having to define them like in the GNS's
-typing freq's with the "1" implied on a number pad vs twisting the knobs is quick
-auto sequencing the missed without the need to un-suspend
-auto VLOC if you are using those approaches, honestly can't remember if the 530/430 did that but was thinking you have to remember to toggle it
-the VNAV function is smarter. In my 530 I got hosed one time as I had the VNAV selected for the fix crossing but wasn't turned towards it so the value wasn't correct and ATC hung me up. As I turned to the fix the VSR value started soaring. Also really like having the VSR on the main screen at the top.
-it shows TOD (top of descent) on the map as a green tick mark
-being able to load multiple approaches if you want to do that in cruise for your alternate for a busy terminal environment.
-Being able to remote the transponder through it, don't recall if that is a function on the GNS
-Having obstruction altitudes displayed on the map
-Having the "flight plan view" or whatever they call it as you build the route so you can clearly see it while building/entering clearances
-When selecting the approach procedure for an airport it zooms out to show where you are coming from and displays all the IAF's to quickly select the logical one
I'm sure there's more but since I haven't flown in so long, I can't remember.
Not saying the GNS's are bad by any stretch, their popularity and longevity speaks for itself and I enjoyed flying behind them in the past. I know people with GNS's can use iPad app's to get around many of these differences (lack of features) but I like having them incorporated into the FMS/GPS box.
