I've got the Hiby R1 and have been pretty pleased with it. The R1 doesn't actually run android but just straight linux. It boots up in about 6-8 seconds and returns to the place you previously were. As for physical controls it's got easy to identify buttons for volume, pause (double click for previous track) and next track that are pretty easy to find in a pocket.

No experience with the R4 but seems to have good reviews with the hifi crowd.