Airsoft Forums UK

They both perform the same function one is metal and on is plastic, then there is the cost.

Check to make sure that teh hop fits your M4, depending on what manufacture you have.

I'm afraid you need to do some home work....

@sneaky is correct in that it's about selecting the right one that works.  SHS do a metal version as well as a plastic version though.  Almost all brands of AEG M4 differ slightly in their measurements.  Do some research on your brand.  Be prepared to experiment a little.  If you buy an expensive hop chamber and it does fit / work you may need to change the nozzle, you might be stuck with it.

fair, its the metal SHS i was looking at. its for a CM16 which firesupport lists as compatable with the laylax

Another option are the ZCI plastic rotary ones. 
Luke at Negative Airsoft highly rates them.

2nd the zci also available from ak2m4,not long fot one myself amazing hop for the cost

3rd, why spend more?  ZCI plastic, see how it works, and only if you have problems buy something else.

ok, you all persuaded me (and seeing the prices on ak2m4) so i ordered the ZCI plastic rotary hop.  they also conveiniently had the 340mm zci inner barrel i wanted and the maple leaf 60deg bucking and nub.  my parts list went from 3 online stores to 1 and much cheaper. 

I also ordered the chrono from them, so we can see if a short raider with a longer barrel gets much of an fps jump.  patrolbase has the L version 10fps higher, so here is hoping. 

(next step is either mofet or cracking open the gearbox and tinkering with that.... that is if i feel the ex rental G&G needs more work)

ok, you all persuaded me (and seeing the prices on ak2m4) so i ordered the ZCI plastic rotary hop.  they also conveiniently had the 340mm zci inner barrel i wanted and the maple leaf 60deg bucking and nub.  my parts list went from 3 online stores to 1 and much cheaper. 

I also ordered the chrono from them, so we can see if a short raider with a longer barrel gets much of an fps jump.  patrolbase has the L version 10fps higher, so here is hoping. 

(next step is either mofet or cracking open the gearbox and tinkering with that.... that is if i feel the ex rental G&G needs more work)

I would short stroke the gearbox and make it a little more snappy. 

That is my go to mod now for all AEG's