Why would I want over 9000 needlers forced down my throat when I should be able to sell the certification? Im trying to understand why there are certifications in the first place if we are going to end up finding them all which will make it feel like we dont have any 
Another question: If their effects are constant, wouldnt having other certs negate them?
Certifications as far as I’m aware are so you can find more of said item.SO for example if there’s a BR with increased reload time and you get a certificate for it you can easily get more.(I don’t have halo 5 atm so I can’t say with certainty that you can get certificates of blues,green gear)
"Another question: If their effects are constant, wouldnt having other certs negate them? "
Maybe you can only have one selected at a time?
I found this while browsing sites thought you might appreciate it" http://www.ign.com/articles/2015/09/18/heres-how-halo-5s-req-system-works
“At launch, there will be more than 1,000 different REQ packs available for purchase with REQ points or real world money. Should you happen to purchase something that isn’t to your liking, you can trade it back at a REQ station for more REQ points.”
You can trade those things that you do not like back for more REQ points.
If my understanding of the certifications is correct, is that they increase the chance of getting that weapon/vehicle in a later REQ pack/packs. If the amount of needlers/battle rifles/pistols in any given REQ is not to your liking, then sell the excess. However, the certifications for items like the sniper rifle or rocket launcher are probably going to be the most anticipated since they are more popular.
On a side note, I think they maybe single use (as in you get it once and its unlocked forever) and after a while it will even out what weapons you get in a REQ pack.
You can have multiple certifications. If you look at your REQ Collection when it releases (if it isn’t already) You can see multiple Certification REQ Cards.
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> Why would I want over 9000 needlers forced down my throat when I should be able to sell the certification? Im trying to understand why there are certifications in the first place if we are going to end up finding them all which will make it feel like we dont have any
Just sell the needlers.
You can trade back in. So if you don’t want a gun you can sell. Nice and neat.