Most of the manufacturers offered a range of options, usually with different lenses & shutters. Top models usually have a Compur or Ibsor shutter with a full range of shutter speeds, while the bottom end models have a 3 speed shutter. Likewise lenses vary from Dagor's, Xenar's, Heliar's, Tessar's etc to cheap and nasty triplets with a variety of indifferent anistagmatic lenses in between.

Often the lenses are the weak link as they are all uncoated, my Ibsor & Compur shutters are still remarkably accurate despite being over 70 years old.

9x12's are usually quite cheap, plate/film holders are easy to find but there is some variation, so make sure you find which type fits. Don't be fooled into thinking all Zeiss 9x12 cameras take the same film holders they don't. Remember Zeiss Ikon was an amalgamation of a few German camera companies.

The glass focus screens are quite poor but Belgium is now famous for exporting Glass focus screen so contact Geert for a better one

Good luck, let us know what you buy.

Ian