So
http://www.theoutdoorshop.com/ (which is conveniently local to me) is having a special extra 15% off everything this weekend which made them on par with Joe Brown and other online shops, so I decided to pop in, get a bit more advice on sizes, play around with Friends and Dragons, and make my Helium Friend purchases.
I came out with Camelots!
There are a number of reasons why:
1) Trigger action
The Helium Friend trigger action was inconsistent, frankly "gritty" in size 1 and, I felt, quite spongy in all sizes; this was not at all what I expected from reading a number of reviews. Mechanically, I noticed one contributing factor: With the single axle design, when you start to pull the trigger, the wires are almost in line with the stem which gives hardly any rotational component of pull on the cams. As soon as the cams start rotating, then it quickly becomes *all* rotational pull. Both the C4s and Dragons, with their dual axles have the wires starting at a reasonable angle to the stem which I'm sure this leads to a more consistent force as the cams rotate, even if the Heliums feel firmer at the start. Having said that, I think the C4s and Dragon bearings are simply better than the Friends. Disappointing.
The C4s' trigger action definitely feels firmer than that of the Dragons and is pretty consistent across all sizes.
2) Handling
To me, the thumb loop makes a lot of sense (which is one of the factors why I originally plumped for the Friends over Dragons) and it felt good on both the C4s and Friends. The Dragons' extendable sling is a very attractive feature, albeit perhaps a double-edged sword, but the Dragon trigger to thumb rest distance just felt too short to inspire confidence.
3) Stem flexibility
I'll be honest and admit that I'd not considered this, but the Camelots have the most flexible stems of the three makes by far - a fact that I hadn't picked up from reviews. I can see this being really useful in horizontal placements.
4) The Camelots just looked and felt like the better all-round package.
So there you go: I did want to buy British, but I'm very happy with my purchase. And it's a good reminder that there is no substitute for having a play with the real thing in a real shop. Excellent help and advice from The Outdoor Shop staff, including a cup of tea and letting me browse competitor web sites to compare pricing... They were, in fact, the cheapest!
The sizes I went for were 0.4, 0.75 and 2, which are overlapping and roughly correspond to 0.5, 1.5, 2.0/2.5 Friends.
Thanks for all the advice in this thread; it was very useful!