I have a PC 7424 that I've had for several years. It has always served me well.
I moved up to a Flex 3401 a couple of years ago and it is a better RO than the PC 7424. Well worth the money if you can go for it. I still keep the PC 7424 and use it for some things, but the Flex is my "Go To" RO now.
RO's are good machines for mild paint correction on cars. It's almost impossible to harm the finish with one. I've used them on my boat, and wasn't really happy with the results. If your Gel Coat is in great condition and you just want to use an all in one product then you might be able to get away with an RO fr the boat, but it wouldn't be my first choice.
For the boat I use my Makita 9227. It's a great little machine. Certainly more money than the HF's I've seen advertised. But detailing is kind of a hobby of mine so I didn't mind spending the extra money.
IMHO: If you have nothing at all to use on the boat and money isn't that much of a factor then get the Makita. If money is a factor, then look at the HF model. I have no experience with it, but several people here have posted in the past that they were happy with it.
Caution: If you are inexperienced then DO NOT go near your car with a rotary. RO's are much better choices for a novice to use on a car. It's ok to start with a rotary on a boat because it's harder to screw it up. Just google for some how-to videos, and you'll be fine.