I've got the F2. At first I thought it was too close to the edge but after using it for a few months I think it's great for small accessories...wallets, pockets, card cases, key fobs.
A 2.5 might be nice for larger items like briefcase and duffles...but you can get by with the F2 for those too.
Yes, I stitch just beyond the crease.
Pic attached of pockets creased with F2, 7 spi. It takes some practice to do curves, just tilt the tip on one end.