Both the multifab and shark suits have air venting valves so they are less likely to invert you - but it is still a possibility.
Offshore helicopter passengers have the benefit of a level of training which gives them awareness of the hasards and instruction in how to use the equipment.
I would recommend anyone who is buying this sort of equipment to at least read through the material if not pay for the somewhat expensive course.
I appreciate it is easy to get too hot in these things - I know I fly more than enough in them! But anything which makes the water more likely to get in invalidates the whole point of the suit. Much as I dislike many of the Channel airports they are the obvious donning, undonning places.