Hi osuorsa! As u can understand from the flag in my avatar, i will talk about Greece.
In the early 80's Greek goverment decided to buy no less than 120 new fighters. Tornado, F-18L, F-16A and Mirage 2000 were evaluated. Some sources state that the F-18L was the fighter of choice, but in the end we end up buying 40 Falcons and 40 Mirages....
The decision, officialy, was based on the fact, that in a possible conflict with Turkey, another NATO partner, the US could embargo Greece, as this has been the case in the 1974 Turkish invasion in Cyprus. So, for Greece having 2 different (totally) sources of fighters, meant that at least at a possible embargo we could still operate the French fighters...
Also, in the tactical level, having 2 types, confuses the enemy. We knew that Turkey was about to buy Falcons. So, they would know the weakness of this plane, but they couldn't tell about the M2000. This proved of vital importance in the following years....
On the other side, supporting logistically 2 types, is costly. Also, the number of the fighters wasn't sufficient enough to let for a domestic production line. It is clearly different to set up a prod line for 80 units and another thing for 40. Eventually we bought another 120 Falcons, but the shortsightness of our politicians, didn't let them to see that the need for a production line was of vital importance.
Overall, you can see that there are somethings you gain and somethings you loose. By the way, the 2 fighters, although they are considered in the same category, each one has certain advantages...for example, matra magic II was far more superior than the AIM9L and it could be launched even when the M2000 was pulling 9 g's, something the -L couldn't . (some nations put magics on their Falcons). Also, the MICA was better than th AIM-120A, and overall the M2000 was better in high and fast interception.
Personally, i believe that we made the right choice. 2 of the finest of their time. But i always wondered what would be if we operated the F-18L, a lighter , more maneuvrable Hornet...