I do like them, but they aren't a perfect panacea. You still have to be careful when using them, but at least they do save on all the extra work of having to haul the weight up to your shoulders to begin pressing.
But working out with heavy db pressing is almost by definition meant to be very difficult. The Power Hooks (what they're called) save you from having to clean heavy db's up, BUT you still have to be very very VERY careful when you unload the db's off the rack. Here's how they work:
You get under a barbell in a rack or at a bench. You have a barbell set pretty high, probably several inches higher than if you were normally bench pressing. You use that barbell as the "rack" on which to rest or hook the Power Hooks.
You've already previously strapped the Power Hooks onto your dumbells. The Power Hooks are thin metal bars with Velcro straps at the bottom. You loop the Velcro straps around the center of each dumbell you're going to use.
(Thus, it might be better to use adjustable dumbell handles, instead of fixed-weight db's, so you don't have to continually remove & strap on the Power Hooks. But either way, if you're changin weights, you're going to have to adjust something -- either strapping & re-strapping the Power Hooks, or adding & removing plates from the dumbell handles.)
The Velcro is on thick leather, and wraps around a few times, so there's no worry about security there. At the other end of the Power Hooks the thin metal bars simply curve over, and you hook this end onto the barbell you have set in the rack.
Now, when you remover the Power Hooks to begin pressing the dumbells, you really have to be careful NOT TO BUMP THE BARBELL OFF THE RACK PINS!!!!! Or else the barbell will smash down into your face. Perhaps you might want to load the barbell with such heavy weight you can't move it off the pins, but this might be even more dangerous, I haven't tried it, I don't know.
When you press the dumbells, you still have to be conscious of bumping the Power Hooks into the barbell as you lockout.
All in all, if anything, using db's & Power Hooks REALLY forces you to pay attention & have lots of body-space awareness! And to use really really good form!
But all in all, they ARE easier & better than trying to use heavy db's the old-fashioned way, by cleaning them before pressing them.
And I'm not really worried about the "thin metal bars" breaking. Steel is a pretty resilient material. You'd have to be a 600-lb barbell bench presser, I'd guess, before you'd have too much weight on the db's to strain the Power Hooks (I've used up to 140 lbs in each hand so far).
You can buy them at APT Pro Wrist Straps --
www.prowriststraps.com