how to choose level shifters for serial / UART
What are you connecting your UART/serial comms to?

The MAX3323 uses external capacitors to generate +5V and -5V, and uses those supplies to convert signals from the low-voltage side into signals which transition between +5V and -5V. It only requires one low-voltage supply to do this.

The shield devices you link to require an external supply ( +5V ) to be used, and will then convert your low-voltage signals into signals which transition between +5V and 0V

The shields will require an additional 5V power supply - and if the device you are connecting to is expecting -5V levels, they won't work.

Edit for use with RockBlock 9603:

The Serial interface on this device looks like you may be ok with 3.3V levels only - in which case no interface would be needed


from here - https://www.rock7.com/products-rockblock-9603