If you are heading into regions where water is plentiful, gravity filters are great. For the Fourth I went with my hiking group to a subalpine lake and used my ULA amigo pro filter to fill platypus and nalgene soft sided containers. I watched my friends go back and forth to the lake each meal to pump water while I made one trip per day to get the gallon and a half of water that was more than adequate for my needs. I find that flowing water works best to fill the bag with the least amount of effort. Camp filtering with the right connector and bladder becomes "set it and forget it" and I can go collect wood, set up the stove, nap in the hammock, or take pictures while it fills the bladder to capacity and stops. I've taken it day hiking and have found that it filters in about the same time it takes others to assemble, pump, disassemble and put away their MSR filters. And if I take out the filter and put in the little shower head, I can have a minute or two of backcountry showering.
However, in fall when sources start to dwindle, a pump filter sometimes becomes easier than spooning or bailing smaller amounts into the gravity filter. I don't think I would want to take the amigo pro into a desert, for example. I have a Hiker Pro (takes the same filter cartridge as the amigo) for trips where water resources may be minimal.
"In the beginner's mind there are many possibilities. In the expert's mind there are few." Shunryu Suzuki
depending on exactly how much water you intend to process, pumping with a modern pump filter goes very quickly. Two of my regular hiking buddies have Katadyn Hiker PROs and those will fill a liter bottle in under a minute, easily.
Loc: Portland, OR
This thread reminded me that I wanted to buy an Amigo Pro gravity-feed water filter from ULA. (Thanks for the reminder, lori!) I've never heard anything but good about the Amigo Pro and all the other ULA products and this filter seems to be right up my alley.
The good news: I got my order in before August 1, when Brian, ULA's owner, shuts down until December so he can get out and hike.
The bad news: Brian just broke his leg, so all orders will be delayed. (And I expect it will play heck with his hiking plans, too.)
I switched to a gravity filter (Katadyn basecamp) this year - I had to replace my old filter, the body of which had cracked - and I like it a lot. When I get to my campsite, I can fill the thing once, then I have all the water I'll need for the night and morning - and more. At lunch stops, it's nice to just hang it instead of pumping. And it uses the Hiker Pro cartridge which I have had good experience with in the past as reliable and easy to clean. I'd never go back to pumping. I took along the bottom half of a plastic 64 ounce apple juice container, which serves as something to pack the filter in, and as a scoop for when the water source is shallow. That worked out well in both roles.
I originally bought the Hiker Pro filter. It worked fine but I really didn't like having to position myself in sometimes precarious positions to pump water. It also seems that everytime you push down on the plunger, the pickup wants to jerk into some debris.
I bought the ULA Amigo Pro and I've used it twice so far. One time was from a tiny creek with only a trickle of water. I'm sure pumping from it would have been a little difficult but I found a spot where the water was trickling over a waterfall. It was easy to fill the bag of the Amigo Pro.
As far as weight, I feel it is lighter than chlorine dioxide drops and here's why. The Amigo weighs eight ounces with stuff sack. Chlorine dioxide I think weighs 3 ounces (and let's say that you prefilter with a bandana that you're already carrying). At a water stop with the Amigo, I can instantly drink and fill up on water and carry less. With the drops you have to wait I think 20 minutes so you're probably going to be carrying that water for a while before you drink it. I think they are pretty even in weight when you consider this.
Then there is the benefit over the drops of filtering out debris and improving the taste.