I've two Sphinxs and two AT-84s (made by a predecessor company of the current Sphinx.)
They're fine guns, typically very accurate and very reliable.
The Sphinxes are subtly different than the ATs; they are, in effect, bargain-priced semi-custom guns, made to much higher production standards than the low-end CZs. The ATs seem to be made to higher standards, too, but not as high as the Sphinxes.
The mags are interchangeable. (They can use CZ mags or EAA mags, or Tanfoglio mags, etc.) (Pro-Mag CZ Compact mags will fit, but won't drop free; CZ factory mags seem to fit fine.) Some parts will interchange (springs, etc.); others might, depending on the part and model.
I can't speak about sights, but they don't us CZ sights. You may have to do some measurements. CDNN had some sights for them, recently.
Its a much better gun than the CZ-85. (I have an 85 Combat and love it, but there's no comparison.)