Is there any meaningful difference between the pro vs glass 1k?
They are somewhat similar, but there are some nuanced differences between them...
Both are very hard, utterly splash & go 1K stones that create little to no mud, and mostly just produce inky metal swarf. Neither are especially fun to flatten, and I wouldn't rank either especially high for their pleasurable feedback. However, both are
very effective stones. As others mentioned, they're both about 15-micron, so more inline with the Naniwa Pro/Chosera 800 grit.
Shapton's sieve tolerances for their abrasive particle sizes seem to be pretty tight compared to most stone manufacturers. This can be a pro, and a con... Pro, if you're doing critical polishing, sharpening straight razors, etc. Con, if you like the 'mixed grit toothy' feeling, that stones with much looser sieve standards give.
The Shapton Glass Stone 1000 HR feels a little harder, and a little grittier under the blade. It's slightly more keen to release abrasive than the Pro 1K (I wouldn't call it mud, as there's not much binder mixed in.).
The Shapton Professional /Kuromaku 1000 feels just that little bit 'mellower' than the GS 1K under the blade, and releases a little less abrasive. It's also unquestionably a better value than the GS series stone.
I slightly prefer the SG 1K on edge bevels. Particularly on somewhat more wear resistant steels, it just seems to have a little more 'bite', and release abrasive to help it keep cutting. I wouldn't say its feedback is better... In fact, it actually has a little more of that 'nails on a chalkboard' type of feeling/audible feedback, than the SP 1K... However, the friction level of the stone feels a little better on harder/slightly more wear resistant steels. It skates a little less, and you can feel it cutting more positively on these materials. It's still not a stone that I would pick for sharpening higher vanadium/tungsten steels (HAP-40/CPM-M4, Elmax, M390, S30V, etc. Like other AlOx stones, it tends to burnish more than I would like, even if it can 'technically' remove steel.), but it does a little better on stuff like SG2/R2, Aogami Super, or simply very hard knives in the 65hrc+ range, etc, than the SP 1K.
The SP 1K, however, I just adore for fine-tuning wide/single bevels. It doesn't load or dish much at all (Even over long thinning sessions.), it doesn't develop mud that erodes the shinogi line or hides any defects. It doesn't glaze, or suffers stiction (Like the SP 2K can on such knives.). It doesn't really generate any contrast between the core/cladding. It drinks very little water, so you don't flood your worktable when thinning a blade (I've never experienced this problem, like
@esoo .). It just cuts. Very fast, and efficiently for its grit, with a very fine and consistent scratch pattern. It's simply the stone I always turn to for thinning work, to ensure I don't have problems that will bite me in the behind later. It just gets on with its work. For the price, and low maintenance, you just can't beat it for this job, in my opinion. I wouldn't consider the SG 1K for this job, even if it actually does perform vaguely similarly, as I have yet to see a performance gain with it in this role compared to the more economical SP 1K.
That said, and at risk of saying something that would go in the 'Unpopular Opinion' thread, I find their strengths to be fairly specific...
I find the edges from either stone to be some of the blandest 1K-ish I've used, if one intends to stop there. I also don't find them to be all that forgiving, or versatile enough to really recommend to newbies as their only stone. Both are stones that always fall into a 'transitional stone' category for me. They're both stones that help you get somewhere, and can do it very well, but they're not necessarily where I at least want to land.
Hopefully this helps...