For starters, this is a nice bag that can take a good punch, high or low kick and some heavy punishment. It's portable and doesn't need to be hung, so there's a lot of nice features if you're looking for a good bag and can't have the noise of it rattling the ceiling.
However, I bought this bag in January and my friend and I knocked it around for four months until the base of the 'stem' snapped. This is the place that gets all the stress, since with a heavy hit the base tips and this hollow plastic stem has to carry the stress of 250lbs of water or sand. (In my case, sand.)
Since, I got a new stem from the manufacturer, but after knocking it around for a few minutes I heard the same crunching sounds at the base of the stem. The hollow plastic stem doesn't hold up, and is the worst part of the bag's design.
If anyone else has had this problem--the solution I came up with was to cut a small circle in the vinyl at the top of the stem and then fill the stem with sand. (There's a small hole at the top of the stem.) The hollow plastic stem now has about 50lbs of sand in it and it feels much better to hit it. The bag doesn't move around, so there's a nice solid feel to the bag, and it's great for strength training. I'm going to add about 50lb more this week, so the total weight of the bag is now 350lbs, which can handle a lot of punishment. Now to see if this can last longer than 4 months! I'll come back in about 6 months with another review.