Hello Ivan and welcome to CN
I have the 102GT and a Orion 100 f/9 ED.
For planetary the ED puts up a cleaner, crisper image at the same mag on Jupiter, the colors are better.
Although the purple on the moon in noticable in the Achro, it does not detract much from the detail I can see.
I feel confident the ED would put up a better image of Mars when it returns, but I did not own the ED when Mars was up last time.
Saturn in not much difference.
I would say overall the ED puts up a 10-20% better image at medium to high power. That is a very hard thing to quantify, and
I don't know how too. I'm sure the experience is very personal too.
Is the ED worth 3-4x the price of an Acho? Only you can decide that.
A 6 inch mirrored scope is a step above the 100 ED, and an 8 inch mirror is a leap.
Both of them can be had for less than a 100mm ED. That is why I stopped buying refractors at 100mm.
Used 100ED can be had for $400, but the 120 ED is a lot more even used.
(Well except for a cheap 120 f/5 I used for a sweeper).
Edited by vtornado, 27 February 2020 - 10:34 PM.