The concept of drop in filters on EF glass is the primary reason for me adopting Mirrorless. I bought my first RF camera body three months ago, the new R8 and this will become my 2nd camera once I've sold my old 5Dmk3's and bought either a R6ii or a R5.
A drop in filter adapter make s a lot of sense on a R8 because the clear filter effectively protects the sensor from dust during lens changing. Unlike the R6ii or R5, the R8 doesn't have a shutter to protect the sensor and it's exposed when changing lenses.
I chose Meike for my drop in filter becuase a) it was a lot cheaper than the Canon...which is frankly a rip off and b) the VND is actually superior to Canon's version. The Meike version comes with a clear filter, which is an expensive option on the Canon version. The Meike has less X shaped artifacts and doesn't have a weird green cast over 8 stops. All VND filters have a slight polarising effect, so careful use is required because you may find that on sunny days and at certain levels of VND, there is polarising going on. Not as much as a pure polariser, but it's there all the same.
These were taken with a ef16-35IIL and the VND:
The reduction in ghosting / flaring with a rear mounted filter compared to quality front mounted filters is very tangible.
The Meike VND has a slight warm colour cast which is actually quite nice. My opinion with any "Neutral Density" is that if you can't have a truely neutral one...at least get one that has a colour cast that is pleasing and you can live with.
These were taken using a EF 135L and the VND used to create a slow enough shutter speed for some ICM:
The Adapter is almost as good as the Canon version and I've read that the filters are interchangable...however, I've not tried this myself. The Meike doesn't ahve the weather sealing gasket around the mount that faces onto the camera. The Canon does, so be aware of that in your comparison.
Since then I've bought a few more filters and their filter cases (which are really nice) and next month I'll be adding their 3 and 6 stop ND filters. I have one box more than I need so I have somewhere to put my clear filter when juggling filters.
Their CPL is excellent and their 10 stop ND is simply the best I've ever used. It's even more neutral than the VND. I'll be ebaying my complete collection of 82mm and 77mm front mount heliopan filters soon. I just won't be needing them going forwards. In fact I'm so pleased with the ND1000, that I'll be ordering their 3 and 6 stop filters next month to complete my needs. These unfortunatly can't be ordered via Amazon, but can only be bought direct from Meike.
I've been using the 10 stop and polariser it with my TS-e 17L and it works great. It's awsome to have a handy, simple and effective filter solution for it. I can even use the ND's with my ef 8-15mm fisheye. Next month, I'll be buying the infamously huge ef 12-24mm L too and that will become my "other" wide lens to supplement my trusty ef 16-35IIL. I'm thinking of selling my TS-e 17L and using a laowa magic shift converter on my 11-24mm instead. That will give me 10mm of shift on an effective 15-35mm range. But that's a subject for a different thread.
I hope this helps! For me, it's EF glass all the way!