KCDW:
There are many reasons, some of which are.
(a) Compact size.
(b) Many features that are constantly being added to
(c) The cones of safety feature is especially neat as you can program it for drift down if you lose an engine when flying over ocean and you are over gross weight for the ferry flight.
(d) With the Ipac the visiblity of the screen is exceptional.
(e) And when you leave the airplane you have a very fast computer that will do just about anything, I have the Targus folding keyboard and I use the Microsoft Word program that it comes loaded with to write a book in my spare time, it is just like having a desk top with me.
(f) Monthly upgrades off your desk top.
However..... they still do not have new upgrades for the Eastern users., everyone outside of N. and S. America.
I have used it in a lot of Europe and except for upgrades to the system it is as accurate as the N. American data base.
If you get one and live in N. America you will need a storage card to hold all the extra features, I am running a 48 meg flash card in an older Ipac and when I down loaded the airport diagrams my card is full.
Chuck