Their problem is more that it's not installed on Mum's phone or tablet. :)
But .. then I tried to use the store to get apps and it was a desert. Or the things I could find, worked poorly.
There's a raft of really cheap (7/8/10 inch) Windows 8.1 tablets that are price competitive with their Android equivalents. At the moment they are running full Windows with an Intel Atom processor. From what I've read, these will all be capable of being upgraded to Windows 10 when release.
Spartan is going to be released for both Windows Phone 10 (or whatever they are calling it) in addition to Windows 10, from what I've read.