I own a sandbag company in Las Vegas, and have manufactured this type of bag for many years.
For the most durable option, purchase a pre-filled bag. Zippers, velcro, and buttons are always going to create a weak point that will inevitably fail. Sewn closure is much stronger, and looks better. Shipping filled bags used to be very expensive and mostly prohibitive, until priority mail flat-rate came around. Almost any company can ship a filled bag for less than $15 anywhere in the USA. My company ships filled saddle bags for free.
The care and handling advise given above is right on: Be somewhat gentle when moving and placing them. Don't store them in direct sunlight. Try to keep them dry. Most bags of this style (especially cordura fabric bags) are very heavy duty - think JanSport. Most videographers that buy them quickly make saddle or flyaway sandbags an essential tool in their arsenal.
