My views can be taken with a pinch of salt seeing as I own none of these products. However on some quick research on this matter. An interesting article which isn't to laborious to read can be found on theroyal geographical society page:
RGS Article
As stated here and on another website selling the Millbank, it appears that it takes around 5 minutes to filter one litre. However it's the iodine treatment that should be left to stand for around 30 minutes; that is the real time killer.
Now although the article listed above states the Millbank bag as unlimited usage in litres. Surely its fibres will clog to a point where by its performance will decrease regardless of cleaning.
On Gear-zone however they have a product which looks suspiciously like the millbank. And it seems they've managed to pluck a 200 litre usage figure from somewhere (The only one Ive found) and stuck it in the pre-product description.
http://www.gear-zone.co.uk/eshop/Water-Purification.html
The MSR Waterworks (WW) and MiniWorks (MW) both respectively give 2000 litres due to the same ceramic (Marathon EX) cartridge which costs, at the moment, £20.00 from fieldandtrek.com.
The only difference between the WW and MW is that the WW incorporates the ability to use a Second-stage PES membrane for further filtering (ofcourse at extra cost). These both weigh in at over 16 oz (with the WW at 19 oz). So the mini is hardly mini
Seeing as though the WW is DOUBLE the price of the MW, its a large price difference just for the ability for one extra filtration level. Obviously not a lot of features for designers to play with on this one for a varying demographic. Not exactly as if you can have a budget version that only screens 60% of the nasties, and a supremo model that does 90%

. They both require the same main ceramic filtration giving the same exacting standards. As this main carbon core removes 'unpleasant tastes and odours caused by chemicals, such as iodine, chlorine, and pesticides' and also 'removes bacteria, protozoa (including crypto and giardia), and particulate'; it appears it does not leave much for the secondary filter to worry about does it!! Infact the MSR website lists no reasons in particular as to having it other than offering a double filtering process

!! I do not believe either that any further purification process is further required (chemical or otherwise) with either the Mini or Waterworks - (going by the MSR website) due to the nature of the ceramic filter utilised in both. So methinks the Waterworks version is for those gear fiends that have to have the best whatever the cost (myself included...god im tempted).
Rant over *sigh*
*new rant*...
Including the initial outlay of £70 for a mini (can be even cheaper if sourced from the states), first time round its economy is 3.5p per litre. On filter replacement (of £20.00 - near enough the cost of a new Millbank bag!) its repeated running cost is further reduced to give 1p a litre. Which to me appears very economical indeed. The Millbank, if kept to 200 litres @ £16.00, is 8p per litre each time. Reminding ourselves of the processes involved in water collection and filtering with a Millbank bag and time involved in waiting for iodine purification, I have to ask, where's the bargain here?
Yes, yes i know....its all about weight!! So theres the new Katadyn Exstream XR Water Filter Purifier. A 3 stage water bottle / purifier all in one, at £30 when sourced from the States. This purifiers maximum usage is stated at 100 litres, and at $19 (£11) (+ postage!) a go for filter replacement, works out at 11p + a litre. With a replacement rate 20 times that of an MSR, postage costs would really add up in receiving cartridges (if there was no outlet store nearby). However weighing in at under 8oz (half that of the MSR's), is it enough Or too high a premium to pay to reduce your load by just over 250g?...
Anyway as stated in the beginning, I know nothing, am probably wrong and most of that marketing bull on which what I've said is mostly based is completely irrelevant in real world practice. Got to start some where though!
Steve