To make it short - this combo filter is very good value for money, as long as you're getting it for the right reasons. While not quite up there with "pro-level" filters in terms of quality, it does a great job for what it is.

Firstly, the main appeal of this filter is combining CPL and variable ND functions onto one - which saves you from having to stack multiple filters (which may end up not working well together) and makes for one less piece of glass between your lens and your target. I've noticed no flaws whatsoever in how the two functions work together - no Xs, no artifacts. The CPL part of the filter is very, very good. The variable ND part is... fine. Better than a lot of filters in this price range. There is still a slight brownish cast from it, but it's totally consistent and very easy to correct in post-processing. Just don't expect stellar results right out of the camera, without a couple of clicks' worth of extra work!

In terms of filter factor, it's more or less spot on - it's a little bit more than 1 stop of light at the lowest setting (ND2), but at the highest setting it seems to be pretty much exactly 5 stops of light - not the 5 and a half you'd get if you took an ND32 filter and put a CPL over it.

However, the real question is: do you need this filter? Because the max setting of ND32 is generally a bit too light for landscape photography off a tripod (you'll want an ND64 or even ND1000 filter there). For longer telephoto lenses (over 200mm focal length), you really don't need this kind of filter for the obvious reason that you're not likely to be getting too much light. For wide-angle lenses, the CPL portion makes it a complete no-go - on anything shorter than 35mm focal length, it'll completely mess up your image with those uneven shadows (not the filter's fault - but CPL is really not designed for that).

So, what is this for, exactly?
Well, I can't speak for video usage - but in stills photography there's one area where this filter really excels, and that is for handheld shooting in bright daylight conditions with large, wide-aperture lenses at the higher end of portrait and lower end of telephoto: in other words, lenses between 80mm and 200mm focal length and f/2.8 or less when wide open. This allows you to really control and thin out your depth of field and shoot at shutter speed that will minimize noise, while being able to control more of the stray light from reflections thanks to the CPL.

I use it for creative photography with just two such lenses, both totally manual: the Samyang 135mm f/2, and the Helios 40-2 (85mm f/1.5). It is very handy with both, really hits a sweet spot for usability despite how bulky those lenses themselves are, and really brings out the kind of extreme subject isolation and bokeh both of them are capable of. So, if you own monster prime lenses of that kind (between 80 and 200mm, f/2.8 or less) - this is a great filter you really will find useful. But beyond those? Might be worth checking something else!

Otherwise, my only other criticisms are about ergonomics: the filter uses some kind of non-standard thread on the outside, and has too little thread left anyway to screw anything over it - so if you were thinking of putting a hood or any other sort of attachment over it, you'll have to forget it. And on too of that, the little "handles" for controlling the ND variation stick out just a bit too far from the body of the filter... so you can't really attach a lens hood behind it either, save for a flexible rubber one - and even then, the "handles" will likely deform it a bit. Long story short - expect this filter to always end up on the very end of your optical train, and expect to have trouble even fitting a lens cap over it without it constantly falling off. It's not a big deal as far as I'm concerned - but you may find yourself putting this filter on and taking it off to store it in a box every time you go out to shoot. Not ideal if you want to put it on a lens and forget about it.

All in all though, I'm very happy with it! Worthy buy and a handy tool to use.