Whoa... You must be <i>very</i> careful working with concentrated acid...

for safety, you
must slowly add the acid TO the dilutant (water, H2O2)
never vice-versa! This is especially important with concentrated acids, as they can get very hot very quickly, even boil explosivley, spraying you with concentrated acid!!!
Be careful fellas... full coverage goggles or face shield is a good idea, as is a chemical respirator, good ventilation, and first-aid supplies on hand, especially and eye-wash method of some sort. Chemicals, especially acids, are no joke... I used to work in materials engineering, and we had one bad accident and several close calls, even with all the safety equipment and procedures of a properly equipped and staffed lab...
Of course we worked with some serious stuff... Nitric acid, Hydro-Flouric Acid and a bunch of other metal etchants, mostly for preparing samples for microscopy. Still, HCl isn't friendly stuff.
I just to make sure all the newbies who read this understand the nature of this stuff!
I don't etch my own boards any more, but I recall being very frustrated with the painfully slow FeCl method. I would've jumped to try a high-speed etching technique with simple ingredients like this.
Anyway, I'm sure it works really well. Maybe if I decide to do my own boards again, I'll try it out.
Safe etching fellas...