||This is my third but first complete gearbox and it is best deal in whole wide world even with shipping for Europe. I have check more than 15 sites.
It gives 400 FPS with my stock barrel (Dboys CQB-R RAS II) and 420 FPS with Madbull VER II 363 mm barrel, DBoys hop up and stock rubber. I have bought Madbull hop-up but do not buy that because it doesn’t feed at all. I have placed review on that but who knows will webmaster approve it 
There are some differences that you can see on pictures and what they say in description so here is my review. Off course I already open it ;-)
Before this gearbox I try all other combinations of parts but I for my “spare” 500 FPS gearbox and other gun I chose almost same parts. For instance tappet plate can be aluminum as nozzle but I don’t like it because of weight and non-flexibility that could break sector gear or some other part. Piston and piston head also can be from aluminum and then you also have more weight and LOUD piston head. Body is tick, strong and nice designed with 8 mm steel ball bearings, SS ball bearing spring guide, Type 0 stainless steel cylinder so you can shoot with inner barrels that have length 510 mm +, double O ring CNC cylinder head that fits perfectly in cylinder and keeps compression very well.
Great AIM TOP gears but I have to shim them and to add some gear grease + they do not have small spring as you can see on a picture or on package. They have regular tubes-distances as all other gears. For me this is better than these small springs, because you do not have wobbling of gears that could destroy them after constant abuse of RC lipo that I use and you can shim them easily as all other gears.
Spring is irregular pitch tempered wire spring.
Very nice 14 teeth piston but piston head is not silent.
If you want silent piston head you should have concave piston head and you have to have silent cylinder head or to remove existing rubber from back side of cylinder head and to add silent dumper rubber. Anyway it is more silent that aluminum piston head and much more silent than my other 400 FPS lipo ready BB gun. Who want to be silent? Make noise as more as you can ;-). BTW compression is GREAT and ball bearing piston head also.
Nozzle have small O ring taht keeps compresion well and tappet plate is nylon also great.
Wires are short, but very tick, much more ticker that some other „upgrade“ swithes that you can buy on market. For me is not immportant because I have XT60 connectors for RC lipo and I will destoy this gearbox much faster than with regular 11.1 V airsoft lipo but ROF is incredible.
My warm regards to all US airsofters from sunny and hot Dubrovnik :)
Rating: [5 of 5 Stars!]