Tesla and Machine guns

CounterStrike5

Campaigns involving Tesla rifles and Machine guns in Africa, I understand that I need to purchase these guns in order to participate. However, what kind of rewards are involved? 

I participated in the trial campaign while I was on the Europe map. I got a reward of 16000 diamonds. 

If I purchase the required tesla and machine gun, how many times will I be able to participate? If I move on to the next map, will I require a new gun or can I go back to the previous map and keep on participating and collecting rewards?