I've dealt with them for several years(bit shorter than RJH) on both suits and dress shirts.
They carry Brioni only for suits not for dress shirts.
I left them a copy of my dress shirts for a exact copy(Did fitting also)
but it was just NOT right. Material is great, but fit and finish is not close to Brini/Brioni's tailoring work.
So, I won't say it's terrible, but not what I expect.
Ascot Chang has been ok for me with annual on site orders over 8 years or so, though the last batch all uniformly had arm lengths slightly too long. We didn't do a remeasurement, so they were going from my previous records. It's not terrible, just not something you expect at this level.
If you consider Ascot Chang, ask to look at the Thomas Mason 150/2 cotton fabric books, which AC claims is exclusive to them.
Since I don't get the monogramming and don't ask for much in special fitting, I'm beginning to wonder what's the point in a made to measure shirt. The special fabric is nice, but not that much better than off the shelf (if you pick the right shelf).