I maybe wrong here, but I’ve always thought this didn’t much matter and that the only reason the Staff might suggest using another iOS device, in some circumstances, is that there might be a device hardware issue, or perhaps ‘pocket fluff’ affecting the mic aperture etc. the tuning outcome should be the same if the devices have been tested, calibrated and approved by Sonos.

I think perhaps one of the more important issues, is to remove the mobile device case/cover, as some seem to leave that in situ whilst tuning, and that ‘may’ apparently affect the outcome.

The easiest answer though must be, if you do have two iOS devices handy, then maybe try both and see which you personally prefer (that’s if there is any difference noticed) and then stick with that for tuning the room(s).