We mostly have RAK833’s though the RAK831 exposes some internal TX/RX signals on the connector which were useful to probe in comparison to node signals when receive window timing (had to tap the TX LED itself on the '833). The '831 also has its own 5v regulator.
The newer RAK2247 has an ill-chosen and entirely unnecessary SPI level shifter requiring slow clocking, but as those may be what are available going forward we now assume a slow clock everywhere. Still have to see if the factory heatsink is removable as we have been mounting the cards against a larger aluminum plate through a silicone pad.
In USB connected schemes the nFUSE implementation of the MCU-on-board idea seems to work though not always in internal mPCIe slots. Definitely avoid the old FT2232 based USB designs which are deprecated.