I've used it on all my new arrivals, including scaleless corys who were no worse for the wear. I'm not sure if it actually works, but I haven't had a fish get sick since using it. I have also had no adverse effects from using it.
Not sure about puffers, but I assume they'd be similar to corys.
I've been given different opinions ranging from "it works well" to "it's snake oil!". Personally, I use it for peace of mind (coupled with a long quarantine period, of course).