each cell is 150grams and 2.4v, so 2 cells is 300grams=10.5oz (about the same as 4200 nimh.)
The size of the cells is 62x95x13mm whereas 4 cell nimh is 44x90x23mm.
Stacking 2 cells would be close in size (vertically, and length wise) to a 4 cell nimh but they wouldn't fit into any current 1/12 car. Stacking 3 cells would be 7.2v, but would also be wider and higher than nimh. When compared to lipo, these cells are more robust, but they are also almost twice the weight.
As long as the cells are cheap, they have potential.