I’ve found them to convert just fine.
On one site, I have cheap-ass players, but on another making over 400 for just one.
For me, it’s approx. one player for every 75 – 100 visitors, which is about average.
While I seem to get a player for every 40 visits from a few programs, I think that’s the luck of the draw more than anything program/casino specific.
Haven’t promoted WJ long enought to assess player retention, tho.