I personally wouldn't go for an inline seat post as I like the forward offset that the pentaclip provides. So if I bought a ti one (well worth it as the steel post is a clunker) I'd get a fluted type. I did everything I could on a budget to lighten my Brompton: seat post is the first priority, then the headset and chainset. After that it's diminishing returns, shaving a few grams here and there which can add up to maybe 100 or so. My Brompton had SA gear cable which is coiled like brake cable: switching that for standard gear cable saved 20 or 30 grams(!).