I have a wi-fi only iPad Mini (posted several times above in this thread), and I bought a Bad Elf Pro Bluetooth GPS. It work like a charm and is pretty much fool proof and dead reliable so far. My wife w. her iPad2 (wi-fi only) and I have both been connected and following a road journey at the same time with no problems (says it will support up to 5 clients).
WIth regard to accuracy (see my comments above and in another thread about location services in a wi-fi only iPad), it is FAR more accurate and responsive than the "wi-fi based" location service natively available on the device.
I have been bemused by how accurate that wi-fi location was, since I live almost a 1/4 mile from my "street address" and well out in the country away from any "hotspots" that I know of. No wi-fi signals EVER detected here except from my router. And yet, my iPad Mini, operating only on its native location service ("wi-fi triangualtion" they say?!?) can put me IN my house on my 3 acre property and sort of tell which end I am in!
I don't know how it can do that, but it does. The pale blue "circle of uncertainty" however is very large, (probably about 100 yards in radius!!) using only the wi-fi location service, however it works!
With my Bad Elf Pro, the pale blue circle around my location spot is about 5 yards initially and, after it has been working a bit, gets even smaller. It can pretty reliably tell me what room I am in in my house. (I'm referring here to my location on the satellite view of Google Maps or Apple Maps).
The device itself is quite compact and easy to carry in a pocket. I"m thinking about putting a velcro self adhesive dot on the back and one on the dash of the rental car we'll be using in Ireland in 6 weeks. By the way, after shopping all the choices for an iPad auto navigation App, I chose Co-Pilot (UK & Ireland) becase it was the cheapest. Trial routes run on it suggest that it is quite good and easy to use and I don't see any reason to spend more for some ot its competitors, though they all look pretty good in the samples.