Congrats!
The M16/AR platform is so cool and so tough.
I love the MP5. The MP5 is awesome and all, but it's like a high maintenance sports car. Sexy...yes. But the ejector spring is fragile and always wearing out, the rollers are always wearing out, the hammer needs special timing, and the bolt is way over engineered and needs an annual physical. Taking apart a trigger pack requires an engineering degree, of sorts.
The M16/AR is American tough. It's simple to take apart. I've never seen an ejector spring wear out. The bolt is darned impossible to break, and if you're out of ammo in a firefight, you can use the bolt as a blunt force object.
Someone mentioned ammo, which brings me to the question I always ask...why do they sell 20 round boxes, when magazines are 30 rounds? It's like the hot dog and bun packaging of the gun world.