I have then and love them. Although our 50 have a "tradewids mast" that is shorter than the taller version, I find the main to be rather large. Having lazy jacks makes it easy to lower the large main. (And with just one zipper I have the main covered and away from the sun.) Being easier also means I'm more likely to take her out for a short sail. Finally, whether I single hand (not yet, boat is still pretty new-to-me) or not, one person can secure the main, quite easily.
The only downside is you really have to be pointing into the wind when raising the main, or else our battens catch on the lazy jacks. This is not really a problem when there's another crew member on board to turn her up at the right moment, when starting from a mooring, or when using the autopilot and engine to hold her into the wind. (I'll have to experiment with doing this single handed.)
Bottom line, love our lazy jacks.