As a retrofit the 540 MAY be ok option, but for new install just get a GTN and be done with it. Lots and lots of reasons but that's the short answer to a long explanation
Here's the biggie though...the IFD units DO NOT exist right now. You can't get one because they're not certified yet. This is I think the 3rd year they are at OSH with the demo boxes, and direct from their July 2012 literature delivery 'estimates' are as follows: "The IFD540 is currently in development and in flight test so we don?t have a specific delivery date but we are driving to an early 2013 completion date. Then regarding the 440: The IFD440 is currently in development so we don?t have a specific delivery date but we expect initial deliveries to be approximately 6 months after IFD550 deliveries".
My point is that lots of people are thinking of buying something based on demo models right now. Until it's certified and you can actually get one, how and why would you choose it?! BTW, we really do like Avidyne, but as most of you know I don't like to sell stuff that doesn't exist nor do I encourage using marketing rhetoric as a substitute for trial and comparison of an actual real life unit. "Savings" on installation downtime comments are a bit dubious at this time - seeing as none have been delivered yet. I'll be glad to do a comparison on real units once the real units are available, but until then having objective discussions on functional comparisons is difficult when the comparison is one real life actual unit that exists pitted against a virtual unit.
Just my 2 cents as usual.
Cheers,
Stein