Toss a coin.
Jet configuration and size with good pump hp ratings will be what he needs to look for. Larger jets, better therapy. Little jets really can't do much.
Motomassage on the Hot Springs is supposed to be pretty good for that. Bullfrog with a jet pack of large jets would also be something to look at.
Sundance, Jacuzzi, Hot Springs, Caldera, Dimension One, Masters, pretty much any of the higher end brands will be well designed for hydrotherapy. He should at least try to dry test (sit in it empty) for fit of seats.
And, of course, be sure to buy from a reputable dealer.