If you're in a hurry, just use foam etching (or the 30 seconds acid bath that I won't go in details about here since it's dangerous and lots of kids might get hurt or breathe it and drown!).
If you plan ahead, you don't need to be in a hurry though
Just etch while you eg. solder something else.
Using a sponge, which is age old (I did that around 4 decades ago), might be ok for large tracks, but you could hurt narrow fine pitch tracks, by scratching the photo laquer layer in a way that either cut the track (invisibly perhaps) or just narrow it more than it can handle.
Personally, I hate ferric chloride, as it stains like crazy - an agitated box of one of the clear solutions in a boxed up bath suits me so much more.