Photo or visual applications?
The ACF system differs from non-ACF with a coma corrector built into the baffle tube of the ACF tube. This is only important when doing wide field photography as it will tighten up the stars along the edge of the FOV. When using a traditional non-ACF SCT, in order to achieve the same result you would need to make use of a focal reducer/corrector that is designed specifically for SCTs. You will also see that these same reducer/correctors cannot be used with ACF optics - you need to use a different focal reducer for these scopes.
For visual, ACF or non-ACF makes no difference. While there is a bee's dick amount of coma in non-ACF optics, you REALLY need to go looking for it while using the very lowest magnification and very widest TFOV the optics can give, and it will be at the very edge of the FOV, and it is not a place where any serious observing is done.
But everyone is different. Me, I only do planetary photography with my non-ACF SCT, so it makes no difference to me, and it I have never really noticed any ill effects those times I visually max out the TFOV of my SCT. But others wouldn't tolerate it, even if the way they use their SCT coma wouldn't be an issue.
In so far a optical quality goes, there are just as many dodgy ACF optics out there as non-ACF, regardless of when they were manufactured.
Ken mentions mirror shift, this is another matter, and the ACF instruments do seem to have this
better controlled than cheaper non-ACF. Not perfect, but better, in both Meades and Celestrons.
Focusing tip if using a traditional Meade or Celestron SCT: Always wind the focuser knob in the same direction to achieve focus. This will also set the object back into the original position you had it in when you focus the object. Wind out, then wind in to focus. Wind out, then slowly wind in.
Also, this mirror shift will affect collimation. So when collimating your SCT with a star test, form your donut, then before analysing the donut, wind out a little then wind in, just like with focusing, and this will leave the primary mirror set in the same place as when you focus
ACF scope or not.
Alex.