Lux (26lbs, 22" from collar to tail) is probably light enough to fit into one of the basic sacks, but I wanted something that would be practical for longer hikes. This bag is great - the hip straps make it comfortable for me to carry his weight and he feels snug and cozy. It took him a minute to get used to it (go slow! warm up over several days), but now he's pretty chill about getting in and out.
Also - I ran into some problems with the delivery, and customer service was amazing. They took care of the issue quickly and were friendly about it, too. Highly recommend!