Have experience with two London bespoke shirt makers - Turnbull & Asser and Sean O'Flynn, and have commented on both in various previous posts
In my opinion (and bear in mind that I have not been a customer of T&A's for 18 months or so, and thus never dealt with David Gale) Sean O'Flynn is superior, in terms of:
- Customer service: Sean is a pleasure to deal with, has a faster and more reliable delivery time than T&A (some of my shirts took 12 weeks with them; the most I have had to wait for with Sean is 5 weeks - and he rushed through an urgent order in 3) and even sends SMSs to let you know your shirts are ready (T&A frequently forgot to tell me)
- Fit and construction: It took T&A 8 or so shirts to get to the point where I was pretty happy with the fit; it took Sean one. After that we have refined and adjusted, but fundamentally, the first shirt from Sean still fits me better than the last from T&A. In terms of construction too, I am happier with the results - with T&A I had a few shirts that had poor seams, and there was an abundance of loose threads. Sean's construction is unfussy (nothing to match Matuozzo or the button attachment on the Foster shirt), but very reliable
Reliability: I had a number of shirts from T&A that turned out nothing like they were meant to (1/2" too big in collar; 1" too long in sleeve; 2" too big around waist). Not sure how this is possible with a paper pattern...
Fabric selection: T&A has some pretty unique (in my opinion gaudy) fabrics. If that's your cup of tea you'll love them. Sean, by contrast, has more classic fabrics from a wider range of suppliers (Alumo, Loro Piana) - some of the cotton/linen LP fabrics are outstanding
In terms of price I think Sean is also a better deal, though I am not 100% sure what prices T&A now charge. Net, I'd add Sean to your list - go and see him, look at the shirts, and see what you think.
One thing though - if you like your collars firm make sure to tell Sean, because his default is to make them pretty soft