Yes, we've tried the Lazy Leash 2.0 and 3.0 (the only difference from what I could tell is that in the 3.0 Lazy Leash version the button that releases the leash is made of something that's sturdier than plastic, which means the button doesn't get stuck as often).
We used them on our medium-sized (45 lbs) Carolina Brown Dog (Lily) as well as our crazy and feisty 40 lb Mountain Feist (Barley). Barley, strangely enough, went into perfect behavior mode on the Lazy Leash. But we figure it's probably related to the style of leash, the sounds it makes, and how that reminded him of the leash he wore during some discipline training he's had in the past.
As for general functionality of the leash - it works on both dogs and my wife loves it. It's especially helpful with our dog Lily who's friendly and we don't mind letting off to roam now and then. But with Barley, who's a tugger, it's not as ideal since the hand-held device isn't as comfortable as the ones on larger leashes.
