I purchased this anchor bag to offset my 80-lbs heavy punching bag. The anchor arrives in a small box in three pieces: the rubber bladder, the canvas shell that houses the filled bladder, and a heavy-duty bungee cord. Installing this anchor is a piece of cake; you simply fill the bladder with the desired substance (be it water or sand), place the bladder inside of the canvas shell, attach the bungee cord to the loop in the bottom of your punching bag, hook the other end of the bungee cord onto the anchor bag's ring, and voila, instant counterweight.
Recommend this product?
A couple of things to point out:
1) The bladder is made of thick blue rubber. The hole to fill the bladder is directly in the middle of it on the top. The bladder itself is shaped like the shell, meaning that it is a cylinder with short sides to maximize the area that holds the counterweight material. As a result, if you choose to fill the bladder with water you need to ensure that you have a flat surface to allow the water to properly spread. If you sit it within a standard kitchen sink, for example, it is wider than the width of the basin and will not allow you to fill it completely.
2) The zip opening on the top of the grey canvas bag which houses the weight bladder only zips open about a third of the way. As a result, you have to be able to mush the bladder to fit it into the canvas bag. Since I filled the bladder with water, it was fairly easy to fit, but if you use sand you may need to be careful; the canvas is not very thick and if you are careless I could see the bag splitting.
3) The bag is actually ingeniously designed in regards to using a liquid as the ballast; in addition to a plastic screw cap (think of a 2-liter bottle's cap), there is also a rubber plug that fits inside of the opening and keeps the water from leaking out and the screw keeps it in place against the pressure of the liquid. Short of a puncture, I do not see this bladder leaking easily.
4) The bungee cord included with the kit is a bit long. In my case, I have the bag hanging in the basement, which has a low ceiling (maybe 7 feet). I had to hike the bag up to the lowest point on the chain and also doubled the bungee cord over, otherwise there would be no tension and the counterweight is essentially useless.
Once we set up the anchor we gave it a go. There was definitely a significant reduction in the amount of movement of the heavy bag, minimizing the "wobble" that results from repeatedly whacking it. There is still a bit of "give", but that is to be expected. In short, this bag is great for a solo workout and prevents the bag from swinging wildly on the hook.
This is what I view as an essential piece of your punching bag workout. The anchor is easy to fill and install, meaning that you will be back swinging in no time and no longer have to worry about the bag wobbling all over the place. The bag can be filled with either sand or water (and I would imagine another substance, if you so desire) and is durable enough to prevent leaks. All-in-all it is a sound purchase and will help you to enjoy your routine even more since you do not have to wait for the bag momentum to slow down again before you strike.