It really doesn't matter so long as the device stays 'locked' to the hand as it rotates.
In my case, I hold it 'like a sword' and most importantly, I keep the grip firm while keeping my wrist 'relaxed' to move naturally. The reason for the firm grip is that you don't want the device to add unwanted rotation inside your grip. It's a trick but definitely doable with practice. The reason I prefer this method is I like being able to remote control iPi Recorder using the buttons on the device.
If you have difficulty holding the controller and performing naturally, then attaching the device to the back of the hand or strapping it firmly in the palm will work. You will need to modify a glove or a strap, and figure out how to firmly attach the device. (Once again, the key word here is 'firm'.)
I've attached the whole device to the back of my hand before, and there is a trick for that too. The problem with attaching it directly to the back of the hand is that the device hits the 'topside' of the forearm when the hand is tilted up. My solution was to sew a foam riser to a fingerless workout glove, and strap the device on top of the riser. This allows it to clear the forearm.
Some users with dismantle the device to make is smaller. This makes it easier to attach to a glove.
FWIW, I decided I was fine with just holding the device, so I don't bother with the glove approach. Once again, the key is way to 'lock' the device firmly, whether that's with a strap or by gripping.
BTW, for head rotation capture, I do use a bicycle helmet with a small foam riser under the device. Here's a picture of it...
http://forum.ipisoft.com/viewtopic.php?f=7&t=10114&hilit=helmet#p22940Before I made this, I used to use a hard hat. This also worked well, but I find the chin strap for the bike helmet is more stable and comfortable. Plus, the bike helmet looks way cooler. :)
Here's a pic of the hardhat rig...
https://littlegreendog.com/2013/04/19/mocap-helmet-update/And an older version of a bicycle hat rig...
https://littlegreendog.com/2013/04/10/one-way-to-turn-a-head/Note the foam pad under the device. Use a dense rubber foam for risers, not a soft spongey one. This helps the device conform to curved surfaces (like a helmet or the back of a glove,) and rest without bouncing or swinging. The thick rubber foam used for gym tiles is a good example; just buy a tile and cut a piece from that.
I also have a Go Pro head band I've been meaning to try for head capture. It
should work...maybe I'll try that today.