I also have a Pur filter (before katadihn) that I use sometimes, but it pretty much sucks for caving. In fact, I'd go so far as to say that any filter with hoses, one of which goes in the water supply and one of which goes on the bottle will suck for caving. It's hard to keep the thing clean and not cross contaminate your bottle with all the shit that gets all over the filter from your hands, etc. A bottle filter would be better for personal use, but doesn't really have the same benefits for the group. When I take a filter along it often gets used by other people as well. I'm not familiar with any of the models you suggested as my filter is 10+ years old. Nor have I researched it recently so I can't really help you there. Maybe there's some better stuff out there now.
I'm kind of a thirsty dude. I sweat alot, and therefore need more water on long trips. I really like having a filter along if I know there's going to be water somewhere, which there usually is. If I'm going to need more than a single liter I often take the filter. A filter takes up the same space an extra liter does, but it's lighter and obviously can render more than a liter's worth of water for the group.
On survey trips that are longer than 10 or 12 hours I'll often have my stove along as well. What can I say, a hot meal will change your point of view on life sometimes.
The slightly bulkier cave pack doesn't really bother me.