Well Vin you asked for "View Points" So here's my $.02!
I have been using the H-Bird 55 since Dec '08 and it is a great unit and I would highly recommend it!
But having said that I have seen all the makes at work Vex,Marcum and H Bird and they all work and all do mark fish and all are accurate.
You need to learn how to set up your machine, how to read it and to trust what it is telling you.
The H-Bird 45 and 55,The Marcum Lx-5 and Lx-7 and the Vex Fl 18 and Fl 20 have similar functions and do pretty much the same job.
As for interference I have fished within 30' of my friends Lx 5 and no issues and a Bud has set up his Lowrance x67 in my portable so within 5 ft of the H Bird and no interference on either unit.
As for the best unit for the $$ and what will work as advertised you will be hard pressed to find a better deal right now than the Lowrance 67-Icemachine, Gagnons had them on for $249 as a door crasher but you can still get them for $279.
On another note!! In '08 when I bought my H-Bird 55 I did not have a fishing boat.
This last summer I bought a boat and am now looking at a Lowrance HDS Gen 2 Likely the 7.
As Terry stated this gives you more options again, GPS with mapping and set up to be portable would be a year round use!!
SaltyDawg Whenever we get Ice here on Simcoe/Cooks Bay and you are in the neihborhood look me up and I would be more than happy to show you the H-Bird in action
Rick