Tiger River is a "sister" brand to Hotsprings (and as Mr Bubbles said, a Watkins Product). They are made in the same factory as the HS tubs, and Watkins is recognzed as a quality maker.
I owned a 2005 Tiger River Caspian and felt for the money it was an excellent value. It was a very good quality tub with some nice features, but nothing too fancy. Insualtion, energy efficenty, quality were important to me over flash and the Capsian fit me very well. My sister now has the tub and loves it.
I can't speak to Sumatrian, but only to Tiger River over all. I do recomend that you wet test the tub to ensure it's comfortable to you, and compare the features and value to other quality names in the same class (Sundance may have comprable tub, and you may also check Caldera (andother Watkins tub).