I would be cautious - 625 gbp for MTM in Mayfair is low, and they do refer to the product as "special order" - perhaps it's just a stock special?
On the bespoke front, from what I've seen in a few videos, the Meyer & Mortimer duo seem to cut their suits (for which they tack on an upcharge to M&M's bespoke price). I would be hesitant to call this the original 'source' for Sinclair-style tailoring, without first learning more.
In Casino Royale he wears all ties from Brioni? T&A shirts and a pair of Ted Baker linen pants yes, that's it. QoS I know nothing about, so you may have right there.
The original source for Sinclair-style tailoring was the man himself, who died in 1992.
The "Anthony Sinclair" available today is a brand created/revived by an entrepreneur, who claims to have borrowed one of the original Sinclair Bond suits for inspiration. I have no experience with this firm, and can't make any claims, one way or the other, about the quality of its product. But even an extremely well-executed copy of the original suit is, by definition, not the "original source."