It’s certainly worth a try. TBH, none of the non-commercial denoisers are all that good simply because the problem is hideous complex. The best denoiser for still and video (in my opinion) is Neat (https://www.neatvideo.com/). It’s available in still and video versions but it’s not cheap. There is a demo available so you can try it out though.
Video Noise is about as truly random as we can imagine. (If you understand the mathematics of random numbers, you’ll know this already) because it comes partly from the sensor and partly from the electronics connected to it. If we’re using compressed video (which most of us are) there’s an extra DCT noise to contend with too - that’s what gives those annoying blocks. (Cineon, incidentally, uses Wavelets rather than DCTs so it doesn’t suffer from that problem).
Most (if not all) denoisers work on the assumption that when you find the noise, you apply a varying degree of blur and smush those noise pixels together. This makes the are more uniform and more pleasing to the eye. This is why you have to sharpen things to polish off any hard edges that got blurred out. The crudest way to do this in Blender is to do a blur and followed by a sharpen pass in the compositor. It works but the results aren’t great.
The best denoisers are the ones that are best able to disseminate noise from detail - which, as you might imagine, is easier said than done.
The simple answer (which isn’t always practical) is to start with the best possible image. As the saying goes, “Don’t try to fix in post, the stuff you should have done in camera.” (and words to that effect.)
With Blender we don’t have that choice, so it’s either buy a bigger computer, send it to a render farm, wait longer or use a denoiser - for stills anyway.
For animation however, you have another option which may be enough: I mention this because (and trust me, I’ve tried!) the results are often better than a ham-fisted approach at denoising.
This panel is your friend.
The clamp settings are for fireflies so that’s probably not your issue at this stage but you see that little clock next to seed? When clicked, that uses a different starting “position” (seed) for the random number generator each FRAME you render. This has the effect of making the noise appear like film grain and you’d be amazed how much noise you can tolerate (way more than you would in a still image!)
You can still used a denoiser to polish this off a little but it’s rarely necessary.
To best look at your particular problem are you up for uploading a sample image so I can give it a go with the masks and set up a project for you?