I couldn’t remember where I saw that so I had to ask the Google…
On further review, the limit appears to be 16 devices rather than 10. The only place I could dig it up with Google was in the News section of the A&H site on the announcements about the release of GLD OneMix and GLD Editor.
The problem with using old iPads is the app might need a greater iOS than it’s possible to have. I have this issue with a 1st gen iPad which can’t be updated to anything higher than iOS5 but QuYou need 7.1 or greater. Shame!