AEP's were originally introduced by the Japanese airsoft AEG pioneers Tokyo Marui (often referred to as TM). Soon after, the Chinese clone factories were pumping out much cheaper copies of varying reliability. The best of the Chinese branded AEP's are made by CYMA, or at least they were until the apparent recent closures of Chinese airsoft factories in August 2009. The beauty of an AEP is that it is rarely affected by weather as it is powered by a rechargeable battery pack. The main drawbacks with AEP's are the limited battery life per charge (around 10-12 mags) and the furious rate of fire in full auto mode emptying the (20/30rd) mag in about 4 seconds! Obviously, firing in semi-auto mode cancels out this 'problem'.