Unmodified vs. Modified Bosch injectors

[Cobra]

I see many injectors for sale (1000cc and the like), some of which are modified Bosch units, and it all seems a little confusing.

Brands like Injector Dynamics sell for double the unmodified Bosch counterparts sell for, and while they're supposed to be the best on the market, what actually makes them better?

Companies like Xspurt, Sonic Performance, Deatschworks all sell modified Bosch injectors, but what do they do exactly, when they're modified?

Raceworks, another mob that sells injectors, also has both modified and unmodified injectors for Barra - both of which are said to flow 1000cc at 3bar and around 1100 to 1150cc at 4bar.

Why would someone buy injectors from another company when Bosch Motorsport sell what they, themselves, manufacture?

I don't mind paying more for better, and when the time comes, I'll trust what the tuner likes to use - but it really does intrigue me, why these injectors are modified when they seem to flow no better than what Bosch sells from the factory.