Smart question. I was hesitant about a 13lb spring too, but it works great with standard loads and really softens the bite. If you've shot an LCP, consider how far and hard it ejects and the (much) heavier spring makes sense. If you're still reluctant buy the 11lb or the 3-pack.
Coupled with the Hogue grips, it really makes the LCP a sweet, easy shooter. A long way from the hand-biter it's born as.
Shoot smart. Shoot S-Mart.