Upsampling as such is not bad. It‘s only considered evil by bit-perfect purists who consider Non-oversampling-DACs best thing ever. Most of the dacs today are oversampling anyway, so that bit-perfect is mostly a myth anyway. If it‘s not upsampled by your source, your DAC will most probably do it anyway.
So, if upsampling is implemented correctly (it is on the iOS app), there is no real negative impact. But it still unnecessary consumes computing power on iOS device and represents an avoidable additional load to the battery. So, I would still prefer if there was no upsampling in the app, but even though it‘s there, the impact is on an economical, not on a SQ side...