Let us look under the dust cover.
The printer had no internal memory or cpu, it used the computers memory with a DMA interface. At the time of release, 1987 RAM was expensive. That is why these printers were cheap compared to ordinary laserprinters but it is also the reason why they printed faster than their concurrents. The interface is fast and the ST had a faster processor to render the image than most printers of the time. A speed of 8ppm at 300 dpi could be achieved text or graphics, the bottleneck was the rendering speed and memory of your ST.
What we see here is the Falcon030 Heatseaker interface for the SLM804 Laser. It connects to the DSP port of the Falcon030. On the ST the printer used the SLMC804 interface on the ACSI port. The Falcon printed even faster because of a different interface and greater speed of cpu and memory.
Lets take a look inside the printer. The green roll is the drum. No scratches should be on it. It still looks alright.