I don't want this to be a specific producer question, but I would like to know if the Sparkmaker is good enough to print small details in OO/HO scale objects. I'm referring here to objects like furniture, and other house appliances at scale. I wasn't able to find any visuals with very small objects for this printer.
In general, resin printers can provide a level of detail that has to be viewed with a magnification device. The technology used in the printer will limit the resolution of the printed object. Laser based SLA printers will give the smallest resolution, while LCD panel based printers can be slightly more coarse.
The specifications on the web site for that printer indicate an X/Y resolution of 57 microns, which is 0.057 millimeters. One-sixteenth of a millimeter is quite a high resolution when it comes to 3D models.
According to the 'net HO scale is 1:87, described as 3.5 mm per foot, a peculiar comparison. Directly related to the resolution of the printer, 0.057 mm becomes 0.20 inches approximately. I suspect that an HO scale model does not require one-fifth of an inch detail level.
OO scale is slightly larger and would pose even less of a concern regarding fine resolution objects.
I own a Sparkmaker FHD whose X/Y resolution is 57µm. Z resolution (layer height) is up to the user, 25, 50 or 100µm being typical values. I have limited experience with it but the level of detail seems to be coherent with the specification.
The more popular (but less powerful in therm of UV light, so slower) Anycubic printers have a 2k screen and reach a X/Y resolution of 47µm. I think some printers with a 4k screen can reach down to 37µm X/Y resolution, even if the practical resolution is probably larger, due to some horizontal light diffusion in the screen upper layers and in the FEP film.