Hi everyone,
I’ve been following this forum for over two years now but never had to say anything I considered relevant for the community, until today 
Next to a Digitakt, I also own several other groove boxes from Korg, Yamaha and Roland, and I’m often trying to find the best-working combination of hardware and iPad/iOS apps for seamless and hassle-free music composition and jamming.
Some may already know the “Groove Rider GR-16” app, maybe the best implementation of a hardware groove box in iOS software.
Now that finally Midi Synchronisation to external hardware including fine-adjustment of latency correction has been added, I’d like to say that it works perfectly and in tight sync with my Digitakt, even over a wireless Bluetooth link (Quicco mi.1 on the Digitakt MIDI port).
This adds synthesis features and FX that complement the Digitakt very well, and I can get as tiny as I like - it’s even compatible with an iPhone.
Have fun!