With 1% more protein, perhaps they aren't finished because they are satisfied with less. Then again, it could be they don't like it as well.
Yucca helps lessen urine odor, which is definitely a plus for indoor rabbits and some outdoor setups.
$5 is a LOT, if you are feeding a good number of rabbits.
Your Blue Seal 17%: Dehydrated Alfalfa Meal, Wheat Middlings, Dehulled Soybean Meal, Soybean Hulls, Wheat Flour, Oat Mill By-Product, Cane Molasses...
Purina Complete 16%: Dehydrated Alfalfa Meal, Wheat Middlings, Ground Soybean Hulls, Dehulled Soybean Meal, Ground Corn, Wheat Flour, Cane Molasses, Ground Oat Hulls...
How do your rabbits act and look? Run your fingertips down the spine, from the head and down the back. Do you feel gentle bumps? Spikes? Nothing? Some commercial lines will have very well-developed loins to either side of the spine, which can make evaluating the spine difficult. Aside from those rabbits, you should feel gentle bumps.
If they're perky, curious, and happy, and the only difference is that they don't eat as much, a few months is plenty of time to evaluate whether they are doing well on the feed. Do they come up and beg for feed if they run out, and bury their noses in it when you refill their feeders? Or do they beg a little, and then halfheartedly nibble when you give them more, simply because they're hungry and this is what they've been given?
If their backs feel good, their bodies feel solid, their waste is normal, they have clear eyes and noses, they're perky, and they're excited to get more food, I'd stay with the Blue Seal!