Interesting view Dan.
I see diving singles as really a twinset split between two people
With a good attentive buddy for diving down to sensible depths with an appropriate minimum gas reserve - how is it not redundant and safe?
Once you're down to about 30m a sensible minimum gas reserve on a single 12 is, for me, somewhere around 90-100 bar - thats when the twinset comes into its own as a extra gas reserve in case you get a FUBAR moment: You just can't get a decent dive and still leave an appropraite reserve of gas.
I wouldn't hesitate to do fundies in a single cylinder rig and then convert to a technical pass at a later date once the twinset comes along. I think you'll find most of the UK Fundies Instructors will happily spend that extra time with you if you've already done a DIRF course with them, helping you with twinset skills at a later date