9-speed - truly Shimano compatable? Any experiences with compact crank and Ultegra ders and the 11-28? SRAM chain in the mix? Thanks

My son just put one on for a century last weekend, performed flawlessly, DA chain, Ritchey compact, DA elsewhere. He used both ends, 11&28, no problems.

Myself and a buddy have both switched to IRD 11-28's. His is 9sp Ultegra, mine is 10sp DA and we both use compact cranks and SRAM chains. No issues for either of us yet after about 5,000 miles each. The IRD 10sp is noticeably heavier than DA but it is worth it to me for the expanded range in mountainous terrain. Shifting is great and the short cage rear will work fine with the 11-28 and 34-50 if the changers and chain length are adjusted properly.