My introduction to Particle.io is a perfect storm of fail. I got a photon in the mail yesterday. (That’s fun to say!) I did get it set up and toggled the D7 LED with tinker. But, today I just have the fast green flashing.
Whatever particle-cli depends on should be forked into spark’s github repo. That’s just sad.
There's discussion about where DFU-util should be placed. In the meantime, this thread contains some links to get your hands on it (forum search 'DFU'):
Just as a follow up, I found that brew install dfu-util works on a Mac. I had never heard of this tool and thought it was unique to Particle. Didn’t realize I could get it from my normal channels until @sej7278 mentioned the source being in Debian Sid.