The dry weight is 8oz for the filter with tubes. There is vitually no water left in it after use, and my thinking is that it's going to be lighter than carryiing a litre of water.
Of course here in the UK, there is probably no real need for one, it's just a case of creating the self sufficiency aspect to a trip.
Is it the 'Vario' you have? I see its dry weight listed as 15oz. Still, as you say, lighter than carrying a litre of water - though you could end up carrying the filter and
a litre of water if your sources aren't too close.
On that tack, when at a water source at end of day or in transit, if necessary before heading off I've sometimes 'force' drank to my stomach's capacity on the theory that it's easier to carry the water inside me. Find I can get in many more miles than usual before needing a drink and so can carry much less water. (though maybe not much help if attempting a speed crossing, due to the internal liquid ballast sloshing around and upsetting your trim!)
Can understand your creating the self-sufficiency aspect of the trip. Seem to get even more satisfaction out of successful trips that have been self-contained. Be interested in your field review of the filter.