My first gravity was the msr system. With it I thought back flushing was tipping my nalgien over and running some of my hard earned filtered water back through which rarely did much. I tried several filters and stumbled on the sawyer. I feel I have the best of all world's now. Dirty bag with pre filter. Good filter and the msr deal that connects to nalgien bottles and about anything else. I do not miss pumping. And the syringe works very well for back flushing.

I have a DIY gravity system bases around the Sawyer Mini-filter. All the good qualities you mentioned. To cut weight/less bulk I don't use Naglene bottles, I use Cantene's.

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I bring 2-48 oz and 1-96 oz.
Lightweight, fold flat when empty, easy to pack.
They can abrade/leak if your too rough with them, but a piece of duct tape seals them right back up.

Gear Review -  Sawyer Filter Bottle and 4L gravity system

The past two trips, I used the Katadyn Combi water filter, along with three 32 oz Nalgene bottles.  The Combi with everything needed, in it’s bag, weighed 28.2 ounces.  Each Nalgene weighs about 6.3 ounces empty.  Total weight of this system was nearly 3 lbs, at 47.1 ounces.
What I liked about the Katadyn Combi:
Taste!  The activated charcoal really did a good job of removing any off taste to the water.
Cleanable filter.  When the Combi got tough to pump, a quick break down and scrub on the ceramic filter got it pumping easily again.
Ease of use.  The Combi has an attachment that screws onto the Nalgene bottles.  Easy to place the bottle on the floor of canoe, or on the ground, and pump water directly into the bottle.
What I didn’t like:
Heavy
Pumping water
Storing capacity.  If I wanted three 32 ounce bottles full, I had to pump each one separately.
Breaking out equipment to pump water while on the move.  It was a bit of a process to get the pump out, attach the hose, screw on the bottle, and pump.  So, when I did it, I would fill all three bottles.  Sounds good, until you hit the portage, and are carrying 2 or 3 full water bottles across the portage.

This year I decided to try a different approach.  I purchased a couple products from Sawyer, the Filter Bottle, and the 4L Gravity system.
The filter bottle is a water bottle with a flip open lid that covers and seals a drinking straw.  The straw is attached to a sawyer mini inside the bottle.  Using it is as easy as taking the lid off, dip the bottle, re-attach the lid, and drink through the straw. 
     The Gravity system has a “dirty” bag that drains through a filter to the “clean” bag below.  The clean bag has a spigot to use to fill nalgenes, cooking pots, etc.  I used some cord to tie the clean bag at the desired height, and a cord with an S carabiner to hang the dirty bag above the clean.  The carabiner is necessary to keep you from re-tying the dirty bag every time you refill it.
I still took 2 nalgenes with me on the trip, but I will probably only take one next time.
Weights:
Sawyer Filter Bottle:  6.9 oz
Gravity system in stuff sack with all accessories needed:  15.6 oz
Nalgene:  6.3 oz
Total weight:  28.8 oz

That is a weight saving of 18.3 oz.  Significant weight saving, and it functioned better!  Granted, I was using a heavy filter, but I would use this system even if it weighed the same, or even slightly more.  Here is why:
No need to pump water.  Ever.
Ease of drinking while paddling.  Nothing to assemble, or take out of bag.  Same as dipping a nalgene, and drinking unfiltered.
No need to portage water.  I still would fill it before a long portage, so I could drink while walking.
Always had water available while in camp.  When the clean water would get low, a quick trip to refill the dirty bag, reconnect, and next time I needed water it was full again.
Ability to do other chores while water is being filtered.  Huge bonus when solo tripping!
What I didn’t like:
Not much.  I didn’t want to take the gravity system down to do day trips, so that left me with boiling water if I cooked a lunch while out.  (I didn’t) But, I did try, successfully, to squeeze the water bottle to get filtered water into another container.  It will work, maybe not the most efficient way, but it will work!
The gravity system is light, but clunky and bulky to pack.
Drinking through the straw did require some effort.  I was concerned before the trip, but forgot about it by day 2.

Overall, I was very pleased with the system.  The gravity system was very efficient in camp, and the filter bottle was very efficient while paddling.  Neither system ever clogged or slowed during the 8 days, but both can be back-flushed with an included syringe if needed.