Personally, those giant valves are a waste of money, I'm afraid. The're too big to be comfortably and safely used on giant balloons, as you really have to stretch the neck of the balloon so tightly, there's risk of damaging and tearing the latex.
They're also of absolutely no use for 24"-36", as they're way too big.
Personally, I would go to a DIY merchants, and see if they have any plastic one-way valves/tubing (in their bathroom and/or kitchen sections) that you can cobble together, for less than £5/$5, which is what I ended-up doing. Okay, it's not going to look great, but it more than does the job, and it's peanuts in monetary terms. A far better solution, in my view.