Hi again.
Yeah, it admittedly isn't cost effective for that purpose :-), but it enhances the functionality of the GPS as well as (most important) the fun I get from them.

Besides the fuel flow data and some engine parameters (all showing on my portable GPS screen) to give, for example, miles to go before running out of fuel or fuel needed to reach a destination, it also serves as a sort of dead reckoning (what boaters call maintaining a DR track): the regular GPS, alone, loses track of distance traveled if there's a GPS problem*, but with this accessory it keeps up with distance (if not turns) that's input from the car until you regain a GPS fix.
[ * For example, once in a while you lose a good GPS fix, either in a city with tall buildings (and sometimes even a heavily forested road) or else when, occasionally I've found, all the satellites are by chance lined up in a straight row rather than scattered (you can see their pattern, called an ephemeris, on another screen) -- for a GPS fix, you need their signals coming from a variety of directions, at least 3 for a 2D fix and at least 4 for a 3D fix.]

Anyway, being a navigation enthusiast (because the calculations are fun), I enjoy playing with my GPS's as much as with my old-fashioned marine sextants -- unlike many, I don't just favor one or the other :-). Some years ago, I was mainly the navigator (though sometimes coxswain) on "facilities" (i.e., the private, members' boats used in service of the USCG Aux)when I was with the CG Auxiliary, and I've taken lots of navigation courses with both that organization and the US Power Squadrons, including Piloting (which is really coastal and inland navigation) as well as what is celestial (or offshore or "blue water") navigation using sextants and chronometers, the latter just for the fun of it because my boats have always been only coastal rated :-).

And yes, I do "play" with my GPS while driving, but much less so than other people that use their phones for texting and such (my GPS also blue-tooths to my phone for calls), so it's not too bad.

Best regards, as always,