I have the Track IR 4, and NO, you won't get $150 worth just for ED.
ED works great, but it has limited forward to back zoom. So the ability to look left or right and then instinctively move my head forward to get a better look at the Left and Right panels is a bit limited. For me, it's simply easier to use a keystroke to bring up the left and right UI's as they give you a tighter zoom which is easier on my aging eyes. So I really only use it to track targets once they fly off forward view which it's great for that. It also gives me the ability to look around while my computer is docking me to the dulcet sounds of the Blue Danube Waltz.
I have Flight Simulator X as well, and in that game Track IR is almost indispensable. FSX 2d panels take up a lot of screen real estate leaving very little outside the plane view. Virtual cockpits are almost required but without track IR moving around views using a hat switch is a PITA. With Track IR, the entire experience is seamless and is as close to sitting in an actual cockpit as can be. look down, see the panel, look forward see out the window. If you need to look up over the panel, just move forward.... and look over the panel. It's difficult to describe in words how much it changes FSX for the better.
To be honest, Track IR in ED is "cool", in FSX it's essential.
I bought the Track IR 4 instead of the 5 for $99.00 and that seemed to be a little more reasonable, since the Ebay deal came with the ballcap (normally 10 bucks). Reviews have said that the 5 is better than the 4, but most reviews say that the 5 isn't so much better as to suggest users of the 4 upgrade. So that tells me, the 4 is "good enough" at 66% of the price of the 5.
I spent 99 bucks and the expenditure improves 2 games I own, one of them is pretty cool (E: D) and one is revolutionary (FSX). So it was a no brainer for me.
As with almost everything, however, YMMV.