new to darktable and editing raws in general. something i came across a couple days ago is that you should not use more than one tone mapper, but search through here as much as i could i wasn’t able to find too much an explanation why you wouldn’t want to do this.
for context i tend to use both agx & filmic (in that order) in my own edits. it’s perhaps a creative choice? i use agx to get 80 to 90% of the look down and filmic for the rest. i had initially started out only using the filmic module, but i find agx’s tone shaping capabilities extremely powerful & flexible. it’s also so useful for nudging colors where i want them. on the other hand, i like the little icing-on-the-cake tweaks i can make with filmic—but especially for the highlight reconstruct, since my style is heavily film emulation oriented.
to use a perhaps flawed analogy, in music production i usually use two tape emulations in the master chain; each tape plugin sounds & behaves in a different way and in their combination i am able to achieve something i otherwise wouldn’t be able to with each individually.
what’s the risk or what’s undesirable about using a combination?
The main purpose of a tone mapper is to squeeze the available dynamic range into a narrower band. They offer a bunch of controls to help you do this in an artistically satisfying way. When you chain two tone mappers, the one on the top (i.e., the one that comes later in the pixelpipe) does not have access to wider gamut that is available in the scene-referred part of the process.
That said, If something works for you and you achieve a result that you like, then godspeed go ahead and keep doing it. There is no right and wrong when it comes to implementing your vision, what matters is that you are happy with what you get.
I would argue that probably you could achieve the same results using a more conventional workflow, but this is not necessarily the case (and, again, it does not really matter as long as you are happy with the result). Why not posting a playraw with one of your edits, so that folks can have a go at it?
The tonemappers adapt the dynamic range by compressing the shadows and highlights to maintain a given contrast in the midtones. They also encode intensities to a log scale ( i.e. I \rightarrow \log_2(I) ). You may not want to do either of those two steps twice…
But if you get the results you want, then the method is correct…