Another update - the QCTP I was trying to buy, didn't happen from the seller I had chosen, so I found another seller (selling the same item) and asked them to price match, which they did - but sadly I was 'stung' for import tax etc via FedEx when it came into the UK from India - an additional £44.28.
So what did I get?
Well, I bought a 10 piece T63 kit from Bluefox_Tools via eBay -
https://www.ebay.co.uk/itm/165543749258 I went for this one as the smaller QCTP, the T51, would only take up to a 16mm tool and I have some 20mm index tools that used to belong to my father who was a precision engineer / tool maker. It seems nice enough made, well protected in the packaging, no nasty burrs, everything seems to fit well and hold tightly, so my first impressions are very good. Once I've used it for a while, I might notice something else but for now I'm happy.
Well, after it arrived it turns out (no great surprise) that the centre height, when the 16mm or 20mm tools are used, is too high, so I can't use it with those tools anyway. I tried an easy modification of extending the adjuster thread (unscrewed the existing stud and replaced with a longer one) but it would mean that to get the tool low enough, there would be only 50% or less of the 'gripping' bit of the QCTP engaging, so would not be very secure. I did enquire with one surface grinding company if they would be able to thin down the base for me a bit, but I nearly fell off my chair when they gave me a rough estimate of cost! Suffice to say, that was a non-starter. The tool post claims to be hardened and seems to be, hence me not being able to machine it down in my (new to me) Astra L2 mill.
The next problem I came up against was that all of my tool post 'stems' were too short, so I needed to make a new one - but didn't have any steel or a 1/2" BSW die. I managed to find a bit of 'scrap' pig iron that will do for now and bought a used tap and die from eBay, so once they had arrived, I could set about turning the pig iron down to the QCTP hole size (16mm from recollection, then turning down both ends to 0.5" dia ready to thread with the die - which might not have been as sharp as it could have been but it seems to have cut clean enough threads.
It's now in place but I haven't yet loaded up my 12mm index tools and set the centre heights on them, but I should have more than enough (currently) and the larger tools I can get the right centre heights with my standard tool post, so I can leave the most common one loaded up and centred, so all I have to do is change the tool post - a 'not so quick - QCTP' if you like!
TLDR: Bought the T63, should probably have bought the T51.