I currently make a commercial, open-source USB MIDI controller based on the Atmega32u4, and I am considering developing a new version that has both Bluetooth MIDI and USB MIDI. The nrf52840 seems like a good candidate for this. I've gotten an Arduino Nano 33 BLE, and have been playing with it a little. However, I wonder if there would be advantages to using one of the Adafruit Boards, or perhaps I should just use the Nordic DK (which would give me the option of using any pins). I'd like to stay with the Arduino environment if possible, because that's where most of my experience is, and it makes it easier for my customers to tweak the firmware. It sounds like the Adafruit Arduino BSP for nrf52840 supports the Nordic DK as well, so that might be the best option for me.
Could someone tell me if there are advantages to using either the Adafruit or the Arduino implementation for this chip? Is one more fully developed than the other? I don't fully understand the differences, other than Arduino runs on Mbed OS and Adafruit runs on FreeRTOS. I've noticed that the IDE is very slow compiling for the Nano 33 BLE-- is compiling for the Adafruit boards any faster?
My project is complicated by the fact that I'd like to have my device be class-compliant USB MIDI in addition to Bluetooth MIDI. Would one platform have an advantage over the other in getting class-compliant MIDI to work?
Thanks very much for your help!