Just my 2 cents: I have a bad elf and like* it (easy to pair and use, good battery life, useful for things besides aviation). I used it with my last wifi only ipad about a third of the time, *BUT the other two thirds I'd just do without it (sometimes I just forgot to charge the darn thing the night before, it was never really mission critical). I do have a mobile battery pack just in case to recharge it, but most of the time it wasn't worth the hassle of getting that all set up just to have a redundant blue dot telling me that I was crossing the same intersection that the 430 was also telling me I was crossing.
Anyway ended up getting a pretty good deal on an iPad Air with cellular, and I think I've used the bad elf once since then just to see how the accuracy held up compared to the built in gps (maybe 1-2m difference). The only thing I don't particularly like is that if you put the iPad screen to sleep the gps chip sleeps too, so when waking up it has to reaquire your location. Not a huge deal, takes anywhere from 2-30 seconds (and again, the 430 is also showing the same info). The bad elf however never loses its lock, so the location info is always available. I keep thinking that someday I might use the bad elf so I've never sold it; in fact it's still in my flight bag. I think I used it to prop up my iPad for a better viewing angle once.
So, I'd go with a cellular ipad if I were you. Much more utility, easier to keep just the one device charged, and t-mobile even has a 200mb/month cellular plan for free. Good for emergencies even if you don't think you'll use the cellular function.