I got the size for 24lbs+. I have 3 in cloth diapers, and my 3 year old who is 32 lbs had a waist circumfrance too large. My 1 year old who is 22lbs fit.
My 3 month old seemed to fit the best, meaning it was able to be fastened all the way. So basically, I wouldn't recommend for over 30lbs
You will definitely need to prep. I washed mine 10 times in hot water before they seemed to absorb much. However, without a booster, these are strictly a 'change as soon as they wet' diaper, because they do not hold very much.
Good for the price, as long as your child is small enough, you prep, And plan to use with boosters and keep up with changes.