The difference is huge because of the difference in materials and construction.
I've been running ePBT 9009 and some GMK keys side-by-side on a switch-testing keyboard all week.
Feel-wise, the GMK feels more plasticy, in a 1990s ABS way.
The ePBT feels creamy and smooth. They have a little more coarseness at first, but it smooths out to near-GMK texture. But the cap surfaces are creamier.
The ePBT is also lower-pitched.
Appearance-wise, the GMK keycaps will be more consistent, brighter, and more lively.
The ePBT is a little rough-around-the-edges, with some flaring at the bottoms of the keycaps. You might have to take a file to some of them, or something. Spacebars and large modifiers may or may not have warping. [Fortunately, it ships with multiple spacebars and other modifiers, so you're bound to get at least one of them right].
If you're going for PBT feel, go ePBT. If you want classic GMK appearance, go with them. It's as simple as that.
Ultimately, GMK produces a more consistent product, with more vivid colours. I assume they are more accurate to the original 9009.
ePBT shoehorned the 9009 colourway into its existing processes, which happen to focus on beige and white keys. [They just had to add some green and pinkish keys].
I find that the ePBT white is 'off-white,' like eggshells or cream. I like it, personally, and it goes with the decor where I am.
But if you're in a brightly-lit modern office, GMK would probably be better. ePBT is more subdued.
