the problem is you never know what workmanship will be like. also these days colour matching can be a lottery.
Due to the materials probably being different, from bumper to wings, you will probably have a very slight variation in colour already in certain lights.
If they take off the bumper and respray it in full, depending on the colour match they can achieve, you may find they want to blend into the wings and bonnet, but it depends on the car really and the bodyshop.
Smart local repairs can sometimes be better, but over time they can then loose thier quality and go cloudy.
There isnt going to be a right choice, both outcomes depend on the workmanship.
Ask to have a chat with whoever will be doing the work. If its a smart style repair, request for the rest of the car to be masked off, or the bumper to be removed while its done, and do not get thier polisher away from the affected area.
If its a full repair, find out exactly what they are planning.
Bodyshops can be so hit and miss, and you cant take thier word for the quallity of work, as soon as some bodyshops get busy, alot of quality control goes out the window, even if you make it perfectly clear how fussy you are.
Id ask if they would be confident in supplying a new bumper, and giving it a full respray off the car, with no blending into wings. Find out how happy they would be with thier colour matching capabilities.
Have a look at it now in the sun as well, see if its already a perfect match from bumper to rest of body, you may find its already a few shades different, in which case this would be acceptable if its the same after they've done the work.
i know my rx-8 has a noticable difference in shade on the front and rear bumpers to the metal work of the car. I'm not 100% sure if this is due to the materials, or if they are sprayed at different locations to the body of the car (which i heard from someone, which may be a rumour)