Can use gently and with care, but not nearly strong enough for serious daily water carbonation abuse
I bought 5 of these for carbonating in 2L PET pop bottles. It worked, I carbonated many 2L bottles of water, but it just wasn't the robust solution I was after.
The first point, following advice found in another review here, is the included cap-to-bottle sealing washers don't work well, so you absolutely need to get better ones. The red EZ Cap Replacement Gaskets sold here fit and work perfectly, excellent, and I was lucky I bought a 12 pack while making my purchase, because the stock washers barely worked.
But here's the deciding issue: the twist-lock Kent couplings won't handle higher CO2 pressures (anything above about 30 PSI) combined with the vigorous agitation needed to quickly dissolve the CO2 in water. The valves in the caps can hold the pressure, but the twist-lock connections end up hissing / leaking, unless you hold the alignment exactly right, and sometimes they even pop off. I found it very hard to hold the CO2 hose and Kent coupler exactly right while shaking the bottle, even using the softest CO2 hose I had. I think the Kent couplings are really only well suited to stationary hookup scenarios, which is not what you typically want for home water carbonation in 2L bottles.
My final system (not using these): In the end, I bought several $15-each, machined stainless steel ball-lock carbonation caps, that have an internal hose barb. I installed plastic down-tubes that reach the bottom corners of the 2L bottles, and the water is both carbonated and dispensed without removing the carbonation cap and losing pressure. For carbonating I used a good stainless ball-lock coupler bought here, which can handle the rough shaking abuse when carbonating (I hold one end of the bottle by the ball-lock fitting). For dispensing I use a cheap plastic ball lock, with a 2" section of hose, coupled to the cheap little Hand Held Beer Faucet sold here. I carbonate at about 70 PSI into refrigerated water, then put on the dispensing tap, and leave the bottle resting on a slight tilt in one of the door shelves of my fridge, rotated so the down-tube is at the very bottom corner. The water is fully dispensed by the CO2 pressure in the bottle, and stays fizzy all the way to the very bottom, because it never loses pressure or gets diluted with air. Just open the door, put your glass under the tap, and fill away. With the stainless carbonation caps, it's an ideal system, strong enough for serious daily abuse for years in a row, and delivering the fizziest water the whole time. These plastic caps just didn't get me all the way there.