It's just like two EQ's. I bought one so I could tune my tower seperately than my boat. I frequently adjust mine present EQ setup when I transition from the boat speaks (ie at the marina during lunch) and the tower speaks (when a rider is at the end of the line). The WS-420 should eliminate the need for these changes so I would suggest it need significantly less adjustment than a standard EQ.
If you were tuning the boat on the water, that is a different story. If you dedicate a half day or so on the water to stereo tuning, you can get it done. If you try to do it on the fly it's a challenge.
Just like anything else (computer, new flat screen TV, etc.) it takes a little time to get it set up but you get out of it what you put into it.