For example, I've had some issues with the legacy Presonus board, especially with connectivity/software/compatibility stuff.
Been running an original 16.4.2 for 7 years. I have two of 'em.
iPad control works fine (although I much prefer being out front with the board). Recording works fine to Capture.
The only downside to the legacy board is the necessity of having a laptop in order to use the iPad. The AI series can go direct to a router as does the new Series III.
If you are considering a legacy 24, then it's the same as the 16 as far as connectivity.