I find the one gallon jugs to be too short to hold the bird correctly and there is danger of them tipping out if they struggle too much. The long 2 gal. jug seems to be just right for a CX or large roo and even better for a smaller bird.
A pic of the 2 gal. in action...imagine if these CX were in the shorter and more slender 1 gal. jugs:


A pic of the 2 gal. in action...imagine if these CX were in the shorter and more slender 1 gal. jugs: