Pricing varies by plan
“And if you already have a Creative Cloud membership, Firefly is already included.”
“I've been part of the Adobe ecosystem for so long and I'm somewhat trapped in it.”
4 more creators cited with it, listed below.
Creators who use this also use

Adobe Lightroom
also used by 4 of them

Adobe Lightroom CC
also used by 1 of them

Adobe Lightroom Classic
also used by 1 of them

Adobe Media Encoder
also used by 1 of them

Adobe Photoshop
also used by 2 of them

Adobe Premiere (Warp Stabilizer)
also used by 1 of them