Gabe Weatherhead, in what I suspect won't be the last of the leaving OmniFocus posts, sums up the fears about OmniFocus nicely:
However, this year has brought some disappointments and huge amounts of resistance to my OmniFocus affair. The OmniFocus 2 for Mac beta left me bewildered. OmniFocus 2 for iPhone is so uncomfortable to use that I simply stopped using it on my iPhone, choosing to enter tasks through Siri and letting OmniFocus add those to my database instead.
That's, in part, why I switched to Flow.