Two different delivery routes
Inhalation puts hydrogen gas into the breathing stream through a nasal cannula. Bathing puts hydrogen into water and puts you into the water. That difference drives everything else: the specifications, the session length, the install, and the maintenance.
Neither one is an upgrade of the other. Comparing a mL/min figure to a ppb figure is a category error, and any marketing that does so is comparing units that do not convert.
Specifications that matter for each
For inhalation: hydrogen flow rate, whether that flow is separated H₂ or mixed gas, purity verification, duty cycle and noise. For bathing: dissolved hydrogen concentration at a stated bath volume, circulation design, priming time and how the concentration holds during a soak.
Both share one requirement — water quality. Inhalers need distilled water for cell longevity; bath systems need sensible filtration and cleaning discipline.
Practical fit
Inhalation suits someone who wants a repeatable daily slot and can sit still for it. It is portable in the smaller classes, quiet enough to work alongside, and needs no plumbing.
Bathing suits someone who already values a long soak and wants the exposure to be effortless. It asks more of the space and the install but nothing of your attention once running.
Cost and household logic
For a single user with a fixed routine, an inhaler is the lower-friction entry. For a household or a spa, a bath system serves more people per session because the exposure is passive and shared over the tub.
Practitioner and resort settings frequently run both: inhalation for individual appointments, bathing as a room-level amenity.