I'd say roughly 7/8 shaves in? Only cut myself on 2/8 shaves so it's going pretty good.
I'm growing my top lip for a laugh but yeah it's quite hard to get at the chin with a straight & i'm still learning so i'll use a mach 3 most of the time but ill give it a go with the straight, have to learn some time!
My straight feels very dull though, i've been stropping on a leather belt, not sure if it's my angle(it might be because most of the time it shaves like a charm!)