Before I start off, this barrel is a budget barrel, and will not net you amazing accuracy and much gain compared to EDGI, Promy, and PDI barrels.
I bought this barrel as a replacement for my Echo 1 G36C. I got pretty bad accuracy woth the stock barrel, and was on a tight budget, so I went with Madbull.
Upon receiving it, I noticed how lightweight it was. The barrel is made out of light-weight, aircraft-grade aluminum. That is why it was so light. I thought for a second that the barrel was plastic.
Installing was a piece of cake, as long as you know what you are doing. The C-Clip notches are a little to narrow, so the c-clip doesn't really lock in, and can make putting the barrel/hopup assembly a pain to put in the gun and remove from the gun. Filing will do the trick though.
I don't know about FPS gain. If there was any, it was minimal and not noticable. Probably no more than a 10 FPS gain. Don't get this barrel expecting a 30 FPS improvement (don't ever believe ShortyUSA's reviews).
Groupings did increase a little. I don't have any exact measurements, but there was a noticable increase in accuracy. This barrel plus a Systema bucking and H-Nub will result in a 140 ft effective range and pretty good accuracy, especially over the stock Echo 1 barrel/bucking/nub.
Cheap, good buy on a budget
Increases FPS slightly
Increases groupings a little bit
Paired with a good hopup, nub, and bucking, this barrel can complete an awesome platform.
Light. Still strong, but makes me feel like the quality is lacking.
C-Clip notches a little too small