I've tried 'em and I knock 'em even though they seem rather popular (because of the price, I presume)
The problem with the washers is exactly that they are hard to put on. Yes, it stops an accidental drop, but makes quickly changing straps a pain. If you want cheap safety just screw the straps permanently on your bass. And it's worse than that. most straps that you didn't have to sell your car to buy have a problem that the hole elongates over time. They become looser and looser until the instrument is falling off the strap all the time. The washers help stop the falling but still don't solve the loose strap hole problem.
I've got both Schallers and Dunlops and Dunlops are my "standard" lock. Both have some problems. Schallers tend to come loose and rotate around. Plus they are big, bulky, and rather hard to use in a hurry. Also the button is sort of squarish so using a standard strap in an emergency, while possible, is less than optimum
Dunlops mostly solve that problem. Recessed Dunlops REALLY look cool on a bass, but then you can't use a normal strap in an emergency, which is why I don't use them. I like the belt and suspenders idea. Dunlops lock positively on the strap (with some effort, but you only have to do it once) and don't come loose. Lots of plusses. The negative is that unless you make SURE they are postively locked, they can SEEM locked but are not. And the bass can drop! My solution for that is to coat the locking mechanism with lithium grease. Makes them MUCH more prone to locking correctly.
I try to make sure that each bass has it's own strap in it's case, but you know how life is. Somehow it's been good that virtually all my basses have Dunlops and I can switch straps in an instant or even borrow a standard strap in a pinch.
This is what I know.
