I used to have a Rivera M100 which is the mono version of the S series, minus the chorus. I had a head and not a combo, and played it through a 4x12 cabinet.
Rivera amps are solid kit, I would call this series more Fender to Modded Marshall in tone vice Fender to Mesa. The tone of my M100 was very woody and thick, not brittle at all. Mids are nicely pronounced but it can do the scooped thing as well. All around this is a very versatile amp and the price for the combo is reasonable, although I would try to get him closer to $900.
One word of caution on Rivera...you cannot adequately assess the versatility and complexity of the amp in a short 1 hour trial run...it will take weeks, even months of twiddling to completely understand how all the controls interact given all the push pull configurations and gain stages. Go give it a run and see what you think, but just keep that in the back of your mind.