i have ar's with and without both features.
my slick sides (no FA, no Dust cover) work just as well as their brothers with those accessories.
i've yet to use the FA on my uppers that have them. none of my other semi-auto firearms have forward assists or dust covers, i dont see what the fuss is about them on ar's for non-battle use.
the one thing i have against FA - if the bolt wont close with out it - somethings wrong. and i need to do more than jam that round in the chamber so the bolt WILL close. like find out if something got into the chaber, do i have an out of spec round, etc.
again - this is discussing NON battle conditions.