The dinghy/lifeboat does have some desirable features however please consider a few points:
I assume you would store the Portland Pudgy on deck. If your boat got rolled over do you think it would still be there? I'm a big fan of storing a proper inflatable life raft in a locker or on the cockpit sole. I will never store a raft up on deck for the reason stated. I survived a roll in mid atlantic (boat did sink) and I'm sure if a dinghy was stored on deck that it would have been ripped off during the roll. I like the idea of the Pudgy but I would certainly advise also having an inflatable on board.
In horrendous conditions the Portland pudgy would easily get rolled over. A proper offshore liferaft has ballast pockets to help prevent getting flipped.
The few dollars saved on having a dual purpose dinghy/liferaft is poor economy in my opinion.