Right.
One of the main reasons the M4 is prefered over the styer by SF is that the M4 does not utilise a piston.If water gets into the piston pot, it can cause stoppages. To the best of my knowledge, the Styer has not failed because of water in the piston chamber.
There are other reasons as well, including faster magazine changes, and other easy to get mods for the M4.
The original F88 had quite a few teething problems, that all new bits of kit have, and its reputation is a bit of a hang over from those early F88 problems. Multiple stoppages in dusty conditions, trigger mech related.
The Butt plate coming off due to SOLDIERS not fitting the rear sling swivel correctly.
There were some problems with the sights as well, and all of these problems have been addressed and fixed over time.
For me, I absolutely hated the trigger guard, made for mittens and blokes with 9" trigger fingers, this also has been addressed, that trigger guard was responsible for 100's of U.D,s.
All up, the new model is good battle rifle with plenty of advantages over the M4, including better balistic performance due to a longer barrel length.
When I did my IET training at the INF centre in 1985, we trialed the M16A2, the Leader,and the F88.
The Leader was the most poular choice among our Platoon, but the F88 won in the end.
Why? Over the length of the trial, the F88 got more rounds on target quicker than the other 2. It wasnt any other reason, than the powers that be thought that the styer was easier to put in the hands of inexperienced soldiers, and have them hit their targets quickly and regularly. The 1.5 optic sight won at the end of the day.
As for reliability,ruggedness,saftey, not as good as the other 2 IMO.