Hop unit

[d4yl33]

Ha all,
Bottom line I am lost, I have a nuprol delta spec ops and the hop unit had a crack through it. Anyway I had a classic army aeg in bits due to the trigger unit packed up first time out. Now I pulled the classic army apart and the hop unit for it is the same as the nuprol, which I am guessing would be due to both being m4 style.
My question is when I was looking for info on the classic army hop unit it tells me it is for a blow back version but I thought blow back is more on gas powered side arms and m4 etc so why is it fitted from factory on a aeg m4 ? And would it work in my nuprol delta spec ops aeg ?
Now side by side there the same and it fits but worried it would mess everything up I will put a link up in next comment post for you to see the unit I am talking about

thanks

[d4yl33]

Apologies guys it has posted twice please see other post for the link regarding hop cheers