The differences between models vary between manufacturers, but some of the differences are:
- Number of tubes
- Double / inflatable floor or single floor
- Canopy or no canopy and type and ruggedness of canopy
- Features like boarding ramps vs rope/webbing ladder
- Contents of the survival kit
I'd expect to see a coastal raft having a smaller amount of survival supplies due to proximity to a coast and probably less time in a raft. With respect to the rest, I can't see the logic in there being any fundamental, structural differences.
e.g. cold water is cold water whether coastal or ocean, therefore I'd always get a double/inflatable bottom. Similarly, wet and exposed crew need a canopy irrespective of proximity to a coastline. In addition, an inflatable boarding ramp is the only effective way for exhausted crew to get into a liferaft, irrespective of being a mile from shore or 1000 miles.
As an aside, I'd also get a model that has a dark liner to the canopy. It's been proven that the fluorescent orange or red has a tendency to disorient the occupants or there's a link between unlined canopies and incidents of seasickness. From my own experience, I know that the darker liner seems to have a calming influence.
Personally, I'd only get a canister version. In a crisis and short handed, I think a valise below decks is adding a great deal of self-rescue risk.
What kind of cruising are you doing and in what temperature of water?
The Viking brand have a more industrial strength 4 person and the "Yachting" version, but they are both very functional.
Yachting - VIKING Liferaft, 4 persons RescYou™ Pro
VIKING Liferaft, throw overboard, 4 persons, type DK+