As far as the strap slipping off the button is concerned, doesn't everybody use a strap-lock nowadays?

Not with some electro-acoustics, unfortunately, because the jack lead has to go through the hollow strap button/jack socket at the base of the guitar. If anyone has a semi straplock - i.e. just one straplock fitting at the top of the strap and an ordinary hole at the foot, I'd be interested in hearing about it.