Yeah, they're standard issue in all Nato survival kits now, I believe. The disposable pocket one is really small and light. I'm sure I read somewhere that independent testing has shown it to be effective for over twice the rated volume, assuming you're not taking it from an open sewer.
The downsides are that it's a bit pricey if you work out the cost per litre, it has a fairly low throughput and it makes your water taste of iodine. Although the last is a feature, not a bug, as it provides better sterilisation. You should leave the filtered water for at least a couple of minutes to allow this to happen. Neutralising tabs (or vitamin C) will reduce the iodine taste.
In short, it's a reliable source of safe water than you can carry in your pocket.