I hate water filled ballast sacs. The bags tear, the zippers break, the liners leak, and the liners seldom line up with the bags. Avoid any ballast that is 2 part, liner and cover. The only one I am familiar with that I like, and felt good enough about to sell, is the Pro X series. The bag is heavy duty with taped seams requiring no protective bag. The fittings are heavy duty and one inch diameter, as opposed to 3/4 inch diameter water bed fittings.
Larry Mann www.HowToWakeSurf.com