Hammer vs Pro-sensor ( paper disk )

[TheCruisinKitty]

Have pretty much decided to get a Spinlock 170N Hammer life jacket but....
is there anything I've missed?

The Plan: 1-2 years of boat deliveries and shakedown cruises in the Med before a transAtlantic to the Caribbean. I'll need to be able to work all positions on 28-40 foot yachts in all weather. In the heaviest offshore weather gear">foul weather gear.

2 Questions:
1) What's the best firing head for an offshore inflatable life jacket for the above plan?
Hammer or Pro-sensor (paper disk)?
Pros and cons?

2) Is there any reason to go for 275N (eg if crew weighs about 140 lbs)? How likely is it to trap air in the all weather gear and need more oomph to turn over in the water? (This is what the sales guy said the 275N was for).

Would really appreciate feedback and others' experiences.
Thanks in advance.