BCM is a great company, don't worry about quality it's hard to find better. They have excellent customer service too so you should get a response from them. Anyway, take a look at this link to see the lengths they go to...
BCM Stuff... - M4Carbine.net Forums
As far as too heavy, too light, upgrades, it all depends on what's right for you. In the standard config, there's nothing wrong with them. If you want lightweight there is a brand new LW middy they're offering now.