They work the same as far as I've been able to tell.
The FeCl3 will heat up a bit when water is added to dilute it if you have a real strong % soln of it.
Not so much with anything under 50% to start with so most of the pre-mix circuit board FeCl3 doesn't show much reaction.
(I believe the warning not to dilute on the lable is about it's strength needed to do the copper etching work it is sold for.)
Some of the circuit board etch sold has a combination of FeCl AND Hydrochloric acid in it.
Probably a bit toothy for the damascus work.
