There are three figures, and the owner weighs all of them: the retail margin on each unit sold, the contribution a treatment leaves after its variable costs, and contribution per occupied room-hour, which is the treatment's contribution divided by its appointment length.
A back-bar product changes the second and third. Compare a treatment using it with the treatment it would replace, on actual product used, practitioner time, other variable costs and appointment length. On stated assumptions, a product that costs more per application, or adds minutes without adding to the price, lowers contribution per occupied room-hour. Any effect on demand or rebooking is a separate question, about total contribution rather than the hourly figure. For a device, the comparison is the equipment and consumable cost against the paid treatments the clinic expects to run, with servicing, downtime and replacement support agreed as part of the offer. A clinic and a product brand keep different scoreboards, and the offer has to read well on the clinic's. On the brand's side, the professional price has to sit on the same ladder as its wholesale and direct prices, and each channel's contribution is judged after training, delivery and support.