i'm in halifax
definately better with RO, in my opinion unless tap TDS is less than 50ppm, RO every time.
my DI vessel is small 6.5ltr, i was using 5ltrs a week in resin. making about 1100ltrs it was costing me £24/wk to have resin delivered.(5ltrs a time) and at the time (i started wfp in Jan) i always had the £24 to order some more, but it worked out cheaper to get the full bag, but i could never spare the £85.
i paid £230 for my RO in march, and it comes out at 1ppm before DI. i changed the resin at the same time. that should be good for around 90,000-100,000ltrs.(18months?) it's 99% more efficient.
the 3 pre filters are about £12 and these need changing every 6months or so. i haven't done it yet. Membranes are 3yrs or so and are £45 each x2 200gpd.
it was a no brainer for me really.