Personally I would say these are only good for short/medium coastal passages in summer. As they say it is a sailing jacket, designed for 7 knots in a sheltered cockpit not 30-40 knots in an open rib.
You really want to think hard about a drysuit, particularly if you go out on your own. Going overboard is a very real possibility in a rib and even in march/april/may you might only have 20-30 mins in the water before it's game over.
Inexperienced passengers give me strange looks when I start donning all kinds of heavy weather gear for a short hop to Guernsey in the middle of august. They know why by the time we get there!