Posted 31 October 2008 - 05:52 PM
The Echo version looks a lot like the one from Big Out (may be the same nub, OEM'd to Echo). The Mad Bull version looks like the alternate one provided with the H nub, that is, very thin side rails.
Of every thing I read about the two versions, most if not all users preferred the black (Echo) version of the H nub. I ran this nub and the stock bucking for a time, and with the 407 prommy barrel; my m4a1 was accurate and fairly consistent.
I just yesterday switched to the DBC 509 barrel and am using the nub that came with the Mad Bull Shark bucking (which I am also using). It looks just like the Mad Bull version in your links; that is, very skinny on the sides. Since I am "breaking in" the DBC, I'll hold off relaying the difference, but will type that the DBC and Shark bucking/nub is already close to (or equal) as accurate/consistent as anything else I've fit in my M4A1. I've got about 500 rounds through the gun; will shoot it a bunch this weekend. So far, I'm very happy with the barrel.
So, based on my limited experience and what I've read, get the Echo or just get the Big Out H nub.
Hope this helps