No, not at a far distance. You would have more luck shooting and compensating than anything else. They are fairly effective at close range.
Seek the services of a good gunsmith
Yes it does have a red dot in the middle of the scope.
No, since it is of inferior quality because it is chinese, if the scope gets shot at, it could possibly crack, injuring your eye.
Unless you have a higher priced or accurate gun, buy high end bb's and take the time to sight it in properly, a red dot or any optics does not do much for the gun.
an electric sight is a "red dot" sight that uses a laser to project a red dot where the airsoft bbs will go when you sight it it.
FN P90 is a CQB (Close Quarter Battle) weapon. The barrel is short (also in the in the airsoft version) so it will not be effective at long range. You don't need scope. You need a red dot sight. Get an Aimpoint M2 (the most common red dot sight for P90), Holosight 551, or reflex sight. Those will suit for function and fit for the look of your P90.
Yes
Never!
rectile is way better enless the red dot is big
The red dot tube is a type of sight or scope with adjustable magnification.
If you don't have a manual, contact the maker.
yes. red dragon airsoft, i at least watch their videos, and their very reliable and helpful. Ive bought guns that they've reviewed, like the Thompson and the STEN, the mp40 and a shotgun, their videos are at least accurate.