Personally, I do not feel the band to be as much as a challenge on leg presses as free weights or the barbell, and I yank that band up as high as I can.
If you prefer to continue doing these with hand weights, go ahead. A set of 10 or 12 pound dumbells is fine, especially for the fast speed Cathe does these at on Gym Style legs.
But if you are happy with the band, then carry on. Just make sure you keep as much tension on the band as you can while you perform the movement safely, and as the previous poster said, the feel of leg presses with the band is different, so it's probably a good idea to do PLB with the barbell and Gym Style legs with the band, and alternate the 2 for max muscle recruitment.
Clare