Here comes the boring bit...
It's not an investment plan, it's whole-of-life insurance, designed to pay out when you die. It's frequently used to ensure that your relatives don't have to find the cash for a funeral. Some people will pay in more than they get out, some won't - that's what insurance is all about.
The one-year delay until cover is granted is simply because they guarantee acceptance, without medicals. It stops people with a couple of months to live taking out the insurance and means that the insurance company can control its risk exposure.
Incidentally, the advert (and the freebie pen) is an almost exact clone of the good old Cornhill Senior Security plan adverts with Peter Purves - Cornhill Life shut its doors about 10 years ago so that the company could concentrate on non-life insurance.