Ideally, on a field camera with limited bellows draw. A field camera also has limited movements compared to a monorail, so you're not likely to run out of coverage. It also weighs only 560 grams. A plasmat lens with a similar focal length would weigh much more. Lightweight 300mm lenses like the Nikkor-M and Fujinon A and C 300mm lenses cost much more, and may not be usable without a top hat board on field cameras that typically have bellows draw of ~300mm.
Kumar