I got the Manncorp RT2100. Dismal, horrible, useless.
To make it workable, you need a way to hold the PCB in place. I machined some magnetic holders that work fairly well. I have been doing fine-pitch printing with it - .4mm. The STP-350 looks much better, although I have not actually seen it in person.
My next step is to add a vision and laser grid above the printer to help with alignment. I have a low-cost setup for that.
Long edge, short edge, or corners work with these little PCB holders. Neo magnets on the bottom hold very well.
Action pic on Manncorp RT2100. Have been 99% successful printing fine pitch. Each PCB gets alignment tweaks.