That seems like a very good deal from that site, and next time I'll try them.
I will be going to Ride-in tyres in Reading for this one, as I owe the bloke big time, he could charge me twice what it costs from that site, and I would still consider myself quids in.
I've never bother too much about pairings either, and will be replacing a Michelin macadam 100 which was on a second-hand wheel I got from the bay, because it had good discs, which has done me for over 10,000 miles.
I do 300 miles a week commuting in all weathers, and the BT23 have always been good to me on wear and handling. I'm loathe to change as I don't want to spend six months for a rear or a year for a front wishing I'd not bothered.