why not buy an android device? my nexus 7 straps to my leg and has gps with wifi only. can probably buy for peanuts compared with apple

You can, if you want. But, how long is that specific Android device working, which OS updates will be offered and how long will it run the current SD software? I have seen so many Androids now gone to the trash bin because their system was outdated and no upgrade offered that I doubt there is an advantage over time.

Horizon Flyer - noted re the cost and features of a new Apple devices vs. Android, but eBay is awash with 'old' iPads that cope perfectly well with SD; the graphics and processors aren't comparable by today's standards, but perfectly adequate for flying. Which is exactly what I use mine for - it lives in the aircraft.

What's the cost of annual subscriptions and updates these days?

Obviously you're correct, but it is worth pointing out that I paid £80 for a re-furbished Samsung Galaxy Tab 4 (8"), and didn't need an external GPS device. All I needed was a yoke mount (from ram mount - they really are good).

The screen is a bit slow to refresh when in planning mode (but for the most part I use my PC for that anyway, and save the route to the cloud ready to open on my tablet). In the plane it works perfectly.

fly4 - I have an ipad2 which barely functions on ios 9. my nexus runs better on android now than when I got it 3 years ago

Exactly - I suppose they're much of a muchness and one's decision is based on previous experience. My old iPad 2 supports 3G (to get the internal and perfectly usable GPS), but no SIM. I also download new routes from the cloud that were prepared on a PC. A nice benefit of doing this just before flying is that all the Wx/NOTAM info is downloaded for the route too.