Capacity is a maximum, not a comfort rating
Some 1–2 person cabins are comfortable for one adult and close for two. Compare interior width, bench length, glass and heater intrusion, and each user’s shoulder width. If possible, tape the interior bench dimensions on a wall or bench at home.
A larger cabin can change warm-up and power
More air and surface area may require more heater output or time. Yet two products with the same capacity label can have different wattage and radiant coverage. Compare actual specifications.
When one person is the right answer
Choose the compact model when the delivery route, floor area, or budget leaves little margin and sessions will nearly always be solo. Keep enough surrounding room for door swing, vents, assembly, and service.
Sources and documentation
Specifications, claims, and installation requirements can change. Confirm the current manufacturer manual for the exact model and variant.