Well I can't answer other options or know anything about the IR5 but I can tell you about my experience with the IR4. I Love It!
I just use the hat clip that goes on a baseball cap, some people prefer the headset clip but I've had no problems with the hat clip. It looks sillier but oh well.
It does take some people some getting used to, I know a lot of people just can't make that transition from a hat switch to just looking, but for me it only took a few days. There are plenty of controls to fiddle with to adjust speed and responsiveness of the IR to your motion, so you can in time adjust it to something that works well for you. Mine has a small "dead zone" strait forward so my cross-hair isn't moving around too much with small movements of my head. Looking behind you can be tricky, but it's just another thing you'll learn with practice.
One thing you'll have to adjust is outside light. I've got to make sure their are no lights shining in on the walls or it'll mess with the infrared reader thing.
But I suppose you're already planning on getting one, so the advice I have is give it some time. Once you play with it enough you'll end up getting used to it and really enjoy it.