I'm using the
Dual XGPS 150 with my adevices (it works just as well with idevices). It looks to be smaller than that Garmin thingee. It comes with a velco wrist strap (good for hooking/hanging on anything sticking out) and a non-slip rubber mount for putting on dash (not attached in any way, secured by g-ravity). But, it only provides a Bluetooth signal for 1 device (as appears to be the case for the Garmin too).
The Bad Elf Pro, on the other hand, provides a signal for 5 devices, but is double-ish the price. If others on board want a GPS signal too, the Bad Elf Pro is the way to go.