I got one of these as a replacement for my old gearbox, and loved it! However, I replaced every part of it, except the gearbox shell, AR latch, cylinder head, and air nozzle. This is NOT because the stock parts are low quality, I just happened to have better parts in a ziplock bag. Anyway, onto the review. I opened the gearbox to see globs and globs of green goop, which E1 passes off as grease. CLEAN THIS OFF! My gun got about 3bps more after I cleaned this gearbox (which means that the "grease" actually slowed the gears down!). The gears are full metal, and appear very solid. Unfortunately, you will have to shim the gears. There was only one shim in the entire gearbox. However, I could not find any wear on the stock sector gear (others got replaced, but the sector MUST be V6-specific, so I kept the stock one) after several thousand rounds. The bushings are (I believe) made of brass, which is better than nylon, but could be better. The AR Latch is solid metal, and has held up very nicely to a 1400rpm setup. The upper assembly of the gearbox was... standard for a Chinese AEG. The piston was some form of polycarb material, but had no metal teeth, which is unfortunate considering the strong spring in this gun. Also, despite the VERY strong spring (I've been told it is an M140), the gearbox only puts out about 380fps. This is because the stock compression is absolutely horrible. Nearly 0% compression between the piston head and the cylinder. I replaced these parts (the stock cylinder was brass, and functioned well enough, though). The stock cylinder head does its job well, and held air when lubricated and fitted inside the new cylinder. The stock air nozzle is clear plastic, but gets the job done. The tappet plate is also clear plastic, so I replaced it with a King Arms one. The stock tappet NEVER failed me, but I was just uncomfortable with the clear plastic build material. The stock spring guide was made entirely of what I believe to be steel, but has no ball bearings (not even washers, which was disappointing). While the stock spring guide was a vast improvement over the plastic one I received in my P90's original gearbox, and I don't think it would break any time soon, I had a ball bearing spring guide (V2, btw) sitting in my room, so I swapped it out. The stock motor has a decent amount of both torque, considering the fact that it is a stock motor. However, it has NO speed. It gets about 900rpm on a 9.6v battery running either the stock M140 or an M100 spring. If you want a high fps, the stock motor is fine, but it can NOT be used for a high speed setup. The gearbox shell itself seems to be made of solid metal (not cheap pot metal used in my A&K gearbox, which snapped in half), and has held up to everything from a 400fps setup to my 1400rpm setup. One complaint I have about this gearbox is the wiring. The wires appear to be VERY low-quality. They are thin and stiff, probably 20awg. My first P90 gearbox came with much nicer wires. I replaced these stiff ones with 16awg low-resistance wiring. Another issue with this gun is the semi-auto trigger contact. Now, this may be a problem with ALL P90's, so don't take this too badly. However, after about 6 months of use, my semi-auto contact wore down (not the contact itself, I suppose, but the little hook that grabs it and pulls it back). Due to this, semi-auto has nearly quit working. There appears to be no way to either prevent or repair this issue. However, like I said, I've heard that this is a problem with ALL V6 gearboxes. All in all, this gearbox is pretty good. The only parts in it that NEED replacing are the wires and the piston. Otherwise, clean it up a bit and you have a pretty good V6 gearbox!
-Decent spring guide, spring, cylinder, cylinder head, air nozzle, gears, bushings, AR-latch
-lack of shims
-No metal teeth on piston
-Clear plastic air nozzle and tappet plate
-Semi-auto function fails after awhile (may be all P90s, not just E1)