We used the service last year and won't be using it this year. As Hussy said it depends on day of week, time of year and even time of day.

Upon arrival last year (a Wednesday) there was no one at immigration so it saved us absolutely no time and since we like to get to Negril as quick as possible we didn't take advantage of the arrival lounge.

Upon departure (a Saturday) it saved us maybe 20 minutes versus the normal lines. The departure lounge was nice but the food wasn't "great" and we don't get hammered at the airport anyway so it wasn't anything special. I kind of like browsing the gift shops and picking up that last bottle of licquor or jerk sauce or coffee or Ting (wasn't in the airport last year).

I'd say save the money and have a dinner at one of the nicer places in Negril.