i have two of these, one for a bass (long) and another for a les paul guitar (medium). I'm 180cm tall, the bass one ended up a bit long, but usable. The guitar one is spot on.
I only play standing. My guitar is a les paul style and, god, it's so heavy, this helps a lot. The bass is also very heavy and it's a godsend, recommended.
unfortunately the leather got a bit loose and I ended up dropping my instrument once, but put some harley benton locks and never had a problem again. no biggie, but watch out :D