I bought the FIRM BSS4 and although it's much easier in comparison to Cathe's HC series, it's a nice change of pace when you don't want to go all out intense.
I can't say whether the FIRM will be better for fat loss than Cathe's videos. The FIRM focuses entirely on combining aerobics w/ weight training. Whereas w/ Cathe's videos, the focus can be either on aerobics+weights, circuits, muscle endurance, interval training, or pure strength training. Both systems have their benefits in terms of fat loss.
IMO, I think it's good to have variety. Also, fat loss all depends upon your genetics, diet, and fitness level. Mix in FIRM videos w/ Cathe's videos, focus on clean eating and you have a recipe for fat loss success!
Eileen