Yes, we have also tested the HAT and software on Odroid C1 and Banana Pi. The problem is that you need to have one of each SBC to compile the software and test it - some of the GPIO pins do not match the Pi scheme, so have to be remapped.
We managed to secure a bulk supply of Pi 3B+, so that suits our market.
Yes I am aware of those projects - you then need to write the software to emulate the printer itself, which interprets the control codes.
We felt it was better to have a HAT which sat on a Raspberry Pi (or other SBC), so we can offer an all in one solution which is portable, rather than sending the data to another PC via USB.
True - it is not designed for 2 way parallel port communication - it just captures the data sent to a parallel port and emulates an old printer (Epson ESC/P, ESC/P2, HP PCL, PostScript, Printronix, Tandy, IBM ProPrinter) - converting the output to PDF which can then be printed or stored.
It was quite a bit later in the history of the printer, when equipment started to expect 2-way communication with printers - obtaining information about the model, ink levels, paper status etc - generally that type of equipment had printer drivers for each model of printer.
We would have liked to implement something along those lines, but there is very little information (if any) about the status messages passed from the printer back to the equipment (it is not covered in the ESC/P2 documentation for example as that was last updated in 1990).
Launch of a small Raspberry Pi HAT which captures data from centronics ports, and emulates an older dot matrix printer to allow for e-printing and printing on modern USB / network printers.
Ideal for extending the working life of older equipment, particularly where the existing printer is no long made, or there is a need to move to electronic paperwork.
We managed to secure a bulk supply of Pi 3B+, so that suits our market.