Larryh, I was talking about the mag extensions from Big Bill's photo, not to mention you gain an extra round as well. Personally, the difference between 9oz and 12oz isn't noticeable in a pocket for me. The size is what I notice. While the percentage difference may be large, both are quite light, and to me, are both far light enough to not be a problem either way. Even then, if you add 1oz with the extra parts, I don't think I could tell you which weighed more when being carried (between 10oz and 12oz). It just isn't much no matter how big of a percentage it may be.
What I notice is size. I can't fit a taller pistol than the stock baseplate in a pocket and holster comfortable. For me, that is the issue, not 2 oz. If I am going to increase the thickness and height, I don't see a reason not to step up to 9mm. I have a purpose for my LCP, but it isn't to bulk it up, but to keep it as small as possible.
I for some reason shoot the LCP pretty well. At 7 yards I hold the 8 ring on a silhouette target in rapid fire. For me, that is perfect. But if I couldn't shoot the thing and had to lengthen and widen it, I would spend the money on a PF9 instead. I really like the LCP, but if you increase the dimensions much, you might as well be shooting 9mm as well.