Photoshop for US$25 without a subscription? That's a bit what Affinity Photo seems like with their current 50% discount (and 90-day trial). And yes, it can support Nik Collection 2.5 by DxO.
If US$25 seems to inexpensive for you, you could also spring another US$50 for the Affinity Photo Workbook, a hardbound book that walks you through the interface, core editing skills (think layers, masks, and more), and then drops into a number of project and technique examples.
I get nothing from promoting Affinity Photo. I happen to use it mostly on my iPad (yes, there are macOS, Windows, and iPad versions), and I like it. I also know a lot of you gave up on Adobe when the Creative Cloud subscription model was introduced but are still looking for something to do pixel edits and layers with. There's no risk here: use the 90-day free trial and see if Affinity Photo is what you were looking for. Make sure to check out their tutorial page for extra help.
