I have an MX20 in my 260SE. It is great - and the resolution is outstanding. Interface is extemely easy to use - almost natural. I have it hooked to a Garmin 430 and couldn’t be happier with how they work together.
Do I wish the MX20 were bigger? Absolutely. It is nowhere near as big as the ARNAV. Do I wish it were the ARNAV? Hmmmm. Having only seen the ARNAV at work for a few hours I’d say so far it is a toss-up, with my edge to the MX20. I think the advantage of size is supreme situational awareness. And if you were suddenly dropped into an airplane in the clouds - and didn’t know how you got there - the ARNAV would be great. However, flying along at 150kts, I find the MX20 is sufficiently large enough to keep me headed in the right direction. And the resolution really pays off when you are talking charts - or even just zooming in to see exactly where that runway you are looking for in the hazy sunshine is compared to your bird. And the terrain awareness is easier to fly with, and frankly, more accurate - which is a nice thing in terrain awareness.
For the moment, if I could put anything in a Cirrus and fly it away. It would be the screen they have in the Lancair. Best of both worlds. Size and resolution. It just seems odd to me to think about spending 200-300k on a brand new airplane and NOT have the best screen available at the moment. Don’t get me wrong, the ARNAV is good, it’s just not the best…