Here is what is said on their website:
With the latest updates our apps RD4 Groovebox and SPC Music Drum Pad for Android are now Pro Audio feature ready. Improvements in Android 6.0 Marshmallow now allow an audio roundtrip latency below 20ms on Android devices which support this feature. The Pro Audio device feature gives our apps excellent response time, comparable to other well supported pro audio platforms.
At the moment devices we know of that support Android Pro Audio are the Nexus 5X, 6P, 9 and the Nvidia Shield Tablet K1, we hope more devices to come soon. For the technical details on what the Pro Audio device feature consists of, read this article on the Android Authority website.