The E&C Handguard (EC-MP501) is a very decent replica of the actual Handguard used on the M16A1 to M16A3 variants. It's tough enough for airsoft use in the field, possibly even on the real steel. It's about a 20th of the price of a real one.
Most airsofters seem to like pimping up their weapons. If you prefer real life military issue authenticity (as a collector, re-enactor or film maker), this is the ONLY Handguard to fit, even if one side of the standard M16A2/A3 Handguard can be adapted and fitted above the rifle barrel with a M203 Ladder Sight (available separately at 18Airsoft) glued or bolted on, as per on the M4. No military used the M203 on a M16 without this Handguard.
The ladder sight opens up to roughly (from memory) the correct acute angle - but can be pulled back further to an incorrect obtuse angle.
Bear in mind that the LMT QD (Quick Detach) Bracket that's usually supplied with airsoft M203s is not backwardly compatible and so CANNOT be used with this type of Handguard. Using an Allen key, remove the QD Bracket, keeping the "H" piece and bolts on the M203 (see pictures). You then need to add the original "U" shaped sheet steel bracket and collets - or improvise them. Even a rough DIY job can be adequate and will be hidden by the Handguard.
I bought the item on a Friday, received it on the following Friday. Mailed from Hong Kong to Britain - this item is RARELY available in the UK. 18Airsoft did a very good job and I look forward to buying from them again. :-)
(HINT: make the short versions of this item and the U Barrel Brackets)