Water ballast works best when it's 'high and wide'... ie all on one side and under the deck edge. Ocean racing boats do it this way, but obviously you need some elaborate systems to transfer the water on each tack, to dump for downwind and refill again.
Not exactly the kind of system you'd want on a smallish trailer sailer.
I have my doubts about the low/central water ballast systems used by Hunter and Macgregor, better than nothing, I suppose, but relatively speaking there's not a lot of weight there and it's not really in the right spot. I do see the advantage for the lighter towing weight.
A weighted centerboard or daggerboard would be my preference from a strictly sailing point of view....
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)