I have several similar to the Life Straw - the Water Straw from
drinksafe systems - and have tried one out on an overnight hike in the Lake District.
How good it is at taking out bacteria I can't say - only that I didn't get ill or drop dead. I'm not even sure whether it improves the water taste, since water from Dungeon Ghyll is beautiful anyway. What I CAN say is that it had no discernible 'chemical' taste or odour, and tasted only of clean, fresh water.
A couple of tips, though:
1) The first time you use it you need a really good hefty suck to get it started. It does get easier, but the effort involved is still more like sucking up thick milkshake than ordinary water.
2) You need a good 3-4 cm depth for it to work properly, so you might struggle with a puddle or tiny rock pool. What I did was scoop up water in my bottle then apply the straw to that.
One other good point for the Water Straw is that it blocks automatically when the filter has expired. Yes, as BP points out, that means a whole new straw - but it does mean there's no risk of you slurping up nasties before realizing the filter's doing nothing.
Like SD, I think there's a place for both this and the pump versions. I have Water Straws in both BOBs, my EDC and GHB, the car glovebox, in a cache between me and my long-distance BOL, and I'm also going to put one in a cache between London and my house. Each one should last a person more than a year - so as Mortblanc says, what's not to like?