The general consensus here is that they are a good gun because
1. they are metal 2. the parts are interchangeable with TM parts and are therefore readily available. 3. An m4 is a good starter platform both for versatility and upgradeability. 4. a m4 is an "easy" gun to work on, getting to the mechbox only takes about 5 to 10 minutes. I have 3 friends with them and 2 have been troublefree, the third one .... not so much.