Shredder has been one of the leading commercial engines on Windows platform during years, though its bright times are over now after the arrival of open source era.
Given that the cost is acceptable, i've recently purchased a copy of Shredder on iTunes and have played two rapid games against Hiarcs which looked the strongest iOS program behind Stockfish. Hiarcs has recently reached 2877 ELO on Rapidroid after first pack of 12 games vs 3 other iOS programs and strong Android engines like Robbolito, Gaviota, Discocheck, Grapefruit.
The encounter used the same opening with both sides: Giuoco Pianissimo: 5.d3 d6 variation (ECO C54) taken from round 1 of TCEC-7. Hiarcs easily shredded Shredder with white but the revenge ended in a draw.
However, the second game looked more interesting to me with clear indication of their different positional vs material interpretations. Hiarcs has dived into a courageous sacrifice which could not birng clear advantage.
My first opinion is that Hiarcs remains one step ahead of Shredder. Shredder showed a perfo around 2700 to me. More games in Rapidroid experiment will reveal the truth.
If you own an iPhone of iPad, should you then buy Shredder? Uhm, well, i don't think you can't live without it, unless you're a dedicated bits and bytes collector.
Now, here are the first two Shredder games played at 15 minutes each side without increment.