Hello ahmed_saleh,
I have a few answers, but they may not be as specific as what you are looking for.
1) It really depends the reason for implementing an orifice into your system. When controlling velocity, the size of an orifice is critical. If you are dealing with a limited plate thickness, then you may have to implement pressure stepping.
2) Restricting orifice plates are usually designed for restricting flow, and are usually not refined (and are less expensive). Flow measurement requires delicate measurements and requires matching of flow rates and measuring pressure drops (usually, more expensive due to the more specific nature).
I hope this answers a few of your questions.
Sincerely,
Eugene