A lot of them make you look like a suicide bomber too, so be careful about running through a built up area wearing it.
I got this one
Make sure you select the 10kg one as they also do 5 and 20 kg versions.
Held up for several weeks worth of use so far, as they go it's comfortable, and seems secure enough. Another one I used to use leaked sand everywhere and I've had no problems with this one yet. Plus it's about half the price of all the fancy branded ones.
I bought mine through eBay and selected to collect it at my nearest argos. Was ready next day.
I know it's pricey but the bulldog weight vest that you can take weights out of I've used for months and it's quality, will last a lifetime and because I'm short and it's short I can do the sit ups without any trouble. It's 20kg but you can take the weights out. I'm wearing it in my picture
...I used to wear mine everyday through the back roads and constantly came across people walking there dogs and the look I got and people walking to other side of the path was beyond!