I second this

They appear to be in parallel, at least that's how it seems when I move the blend knob. So you cannot choose one over the other to come first that I can tell. I got it used so I still need to look up an owners manual.

I'm looking to add a compressor to my board, how do you like the Keeley?

It's basically a fat rat clone. It's been a solid pedal.

I don't usually stack them. I use the switch blade to either have an OD with fuzz/splinter in parallel, or I run the splinter into the plumes in series.

I like it. Having a bias on a tone bender circuit and fuzz face is a nice add.