The better tailors can exactly match any garment you bring to them. Most of the work is done in Shenzen (across the border) so it takes a day or 2; on-premise is final tailoring plus the initial measuring which are the higher skill parts. I've had Danny's replicate an Armani 19th century style opera shirt (silk with white tail collar and no buttons) which they did perfectly, even matching the fabrics correctly -- everything but the label Hong Kong is particularly good at this kind of service, plus the fabric selection and prices are great (better than you will get in Milan for Zegna fabrics, for example).

I was initially skeptical about Hong Kong tailors, but have found them to be great. Almost up to London Saville Row standards at the top end, for a fraction of the price and done in days rather than months.