I really wish Merrell would make half sizes.  I'm a solid 8.5 medium, and usually when I buy shoes that don't come in half sizes, I size up.  In this case, the 9s were way too big.  In particular, the strap that goes around the heel was way too long for my narrow-ish ankles, and the velcro is placed such that if I tightened them adequately, I had a substantial strip of leather left over not attached to velcro.  There are separete adjustments on each side of the heel, and I had to adjust each to its maximum narrowness to make them fit, and this left both ends sort of flapping loose.  I thought about trying an 8, but given how big those back straps were, I was doubtful that they would be OK on the 8.  It's a shame, because the footbed seems SUPER comfortable.  Really cushy, and great arch support.  I can't speak to how long I could comfortably wear them, as I've sent them back, but I'm pretty sure they'd be really comfortable.