Just returned from 5 days on a Hunter 410 with 5 guys and two vacuflush heads. They worked as advertised every time, and we ate well and gave them a good "challenge" each morning. No smell, and the holding tanks lasted for the full days.
Bad point - noisy when flushed. If someone gets up in the middle of the night to use the head, everyone in the boat will know. First person to use it in the morining wakes everyone else up with the noise of the vacuum pump and the gurgling of the waste being sucked around several 90 degree elbows.
Overall, I wish I had the $ to put one in my 35 footer this year, but that will have to wait.