Yes, I use Frigate+.
It sorted out a few false positives and false negatives I was getting (shadows and trees detecting as people, etc). It will be very case by case... if you don't currently have accuracy issues, then it won't be worth your while. But if you do get false negatives and positives, it will definitely sort that out.
I basically get zero false positives or negatives on people anymore. I do sometimes get babies on all fours being detected as dogs, and it can mix up animals sometimes - but I haven't trained that out. I focused the training on people detection, and it works great.
It's a once of fee - not a subscription - which is nice. You pay for a set of 12 model trainings (you can train as many pictures as you want per training). But you're not locked into paying it forever if it doesn't work for you. You also have permanent access to any models you train, even if you never buy another set of trainings ever again.