The strap is worth the money just as insurance. The case strap is way to small for the average guy. If you're a child/teen, women or a really small guy then you might not need the strap.
I'm a big guy (6'1", 230lbs.) and most armbands for mp3 players. This was a must have and works great. Only complaint is if I'm wearing a tank top, the velcro can rub against my ribs/armpit, which can irritate. but I usdually turn the band so that doens't happen. Great product and arrived quick.