Terrific device - you can connect it to anything with a TX serial line (like Raspberry Pi) and it will work right away. I'm gonna use it for an old computer with TAPE IN line and some retro kits, and I'm really happy about the ease of use of these displays - even if a computer has no UART, you can just resort to bit-banging. Basically, an alphanumeric display on a shoe string. Oh, and of course it's great just for monitoring and debugging serial lines, as advertised.
Amazing customer service - just one example of many: I asked if I could have some of these displays at the rate of 2,400 baud (for old computers) and the seller was really nice to customize some displays.