I ended up going with EDTracker. It seems to be working pretty well so far.
I will embarassingly caution other American buyers that £ is not the symbol for euros, it's the British pound. The exchange rate between USD and GBP will be fairly shocking on your statement if you were expecting the USD and EUR exchange rate.
I feel slightly less secure in the purchase because if something does go wrong, it will be a greater hastle to sort it out than if I had purchased the TrackIR 4 from Amazon. Previously I had thought I was saving about $20 by going this route, which was part of the justification, but they ended up being the same price after the conversion.
Overall I'd say the EDTracker implementation seems more practical to me than the TrackIR implementation; I'd rather not have to have a webcam staring at me for no reason all the time. The USB cable coming from the top of my head might get annoying, but I'm buying a longer cable and some clips so hopefully I can get a more comfortable slack going.
So far I'd say the biggest issue I had was with the magnetometer calibration for two reasons.
First, even though the EDTracker Pro offers a sturdier USB port, it's still a USB port. Even the best will still be relatively fragile. Having to twist it all around while it was plugged in felt like I was taunting the USB port gods. I followed the video, which moved kind of fast. I'm not sure what pace you need to go for the calibration to be valid, but if you can do it more slowly, I think it might be better to let the user know that and maybe offer a way to slow down the video as well.
Second, my headset's ear cups can swivel, making it fairly difficult to replicate the motions of the video (again, a slower pace would have helped). It might not sound like it would be difficult, but if you recorded a person calibrating a headset with swiveling ear cups, you could play Yakety Sax to the recording and it would fit very well. That's the only adequate metric that I can think of to describe the degree of fumbleness involved.
I think EDTracker is the clear winner for British players or anyone who might have a more favorable exchange rate. Once the price gets into the $80 range it's a bit more difficult, but overall still a good deal.