I do not consider this a particularly generous offer. With AFKL you get life-time Platinum status after 10 consecutive years of Platinum status. This means you will need 700,000 miles. For most frequent flyers 700,000 miles with AFKL will be easier to achieve than 500,000 miles with Korean Air or Asiana. Simply because Asian carriers tend to have the least generous FFPs.
(Of course, it's not a bad offer either. If you cannot distribute the 700,000 miles more or less evenly across 10 years time, 500,000 miles life-time might be easier.)

[Remark: I was considering going for Asiana's *A Gold for life as my AFKL Platinum for life is almost reached, but I was put off by the low amount of miles you earn with them. Taking into account the loss of money that this entails, I came to the conclusion that it is cheaper for me to qualify for *A Gold on a regular basis with a FFP that is more generous than to go for the 500,000 Asiana miles.]