as far as success, i've had good success with this stuff. i've not used anything specifically labeled "marine" though.
automotive: i used the DupliColor brand to change the interior of my Rubicon from khaki to a two-tone black and gray. success really comes down to prep/patience just like regular paint. the Jeep's interior has held up really well for the past 3 years. there has been some fading on the cloth seats, but that should be an easy touch-up. the panels were removed, washed thoroughly with soap and water, sprayed/wiped with Prep-All, tack-clothed, then got at least 5-7 very light coats of the dye. this is where i believe most people go wrong - very, very thin coats seem to be the key to longevity, otherwise it can lift/peel up. they were left to dry for several days. these dyes get a lot of poor reviews, but i believe if you're not impatient and are very careful, you'll get good results every time. the cloth seats were very easy: i removed the cloth and ran them in the washer before spraying them. btw, cloth seats use a lot of dye!
marine: a prior owner replaced my swim deck seat backs with the wrong color - the center area was a light sea foam greenish color from another year, but all my other seats are the white/gray scheme. so i removed and washed the seats thoroughly with soap and water several times, using a toothbrush to get into the stitching and under the piping. then i "surgically" taped off the white areas with good quality 3M painters tape - this took the most time because i used a large sewing needle to work/bend the tape over and around the individual stitches so it would look factory (basically did my best to tape over the stitches so they would stay white, but still allow dye to get to the very edge of the vinyl). instead of using Prep-All, i carefully wiped the area with acetone. you have to keep enough acetone on the paper towel so it doesn't dry up, but not so much that it runs/bleeds the old color everywhere. follow with a tack cloth and you will have a clean and prepped surface. i think i did 3-5 coats with the VHT brand. mine came out better than i had expected. it's not an exact color match, but no one can tell it isn't OEM because these panels are not next to the main interior. i use the 303 vinyl cleaner and UV protectant on them and they have been holding up great since spring.