By robust, I mean something that isn't likely to break if accidentally dropped or break during operation. Does the Pocket have a plastic housing? I could be wrong but I thought it was aluminum.

We often times let the water settle overnight and I have used the old Sweetwater prefilters. Both help with my MRS/Sweetwater Gaurdian but the Hiker Pro still pooped out after 4 days.

I can see where the gravity filter systems would work well for some. However, most of the time, we filter when taking a quick potty break or when scouting and/or portaging (kayaking) so don't have time to set up a gravity system and wait. To save weight, we carry minimal water (27 oz) and filter as we need.