Without knowing anything about the nature or severity of their arthritis, it is impossible to give you an answer. Honestly, I would say that it's a nice idea, but generally it's not helpful to purchase specific medical devices for other people without their direct input. No two situations with the same medical problem are identical.
Can I suggest maybe a gift card for a store that specialises in rehabilitation / adaptive equipment and giving them the catalogue? Those kinds of businesses tend to be... extremely expensive though, so be warned. Companies love preying on people's desperation.