Kent Fittings - Shut-Off Male Quick Disconnect (QD) x Soda Bottle Cap

Just wanted to add my experience with these caps. The washers truly suck. It is frustratingly difficult to get a good seal every time I do a refill. The washers are just too big and will hang on the threads nearly every time. You have to push them down snugly to get a seal. That sometimes takes several tries.
Now looking for a washer replacement.
My experience with MoreBeer has generally been very good. This is a surprising disappointment.

The title kind of says it. I was very frustrated trying to get these to seal till I discovered that cam-lok washers, of which I had a lot of spares, fit and work like a charm. Others have had good luck with EZ cap washers. Either way the ones that come with it suck and I wouldn't even bother trying to use them.

With original washer one star with a replacement five stars

I have lots of experience at bottle conditioning beer but none at kegging or force carbonation so I can't really make a qualified comparison between this product and the corney keg adaptations. However, I'm very happy with this gadget! I took Dan's advice and included a pack of EZ Caps on my order along with two cap and female QD sets plus two more caps. The seals included with the cap proved to be ineffective on the first try so I switched to the EZ Caps - problem solved. Good call Dan! I've found that either type of seal will fall right out of the cap and on to whatever lies below, so I just make sure that I'm ready for that. I got the second female QD so that I could put a short piece of tubing on it and use it to flush the male QDs on the caps. The quarter turn required is just too easy! I can't imagine a ball lock connection being any easier unless you like leaving the hose connected to the bottle while your shaking things up. I thought about going with a ball lock system for that reason but I would have wanted an additional pressure gauge between the check valve on the reg. and the corney keg coupling in order to monitor the pressure on the bottle end of the system while shaking it up. So far, I like being able to shake two bottles at the same time while adding intermittent shots of CO2 until they won't accept any more. I can spend the pressure gauge money on more caps! My reg. is set at 40 psi. and these shut-offs don't seem to be leaking at all. This makes for smooth sailing when switching the hose from bottle to bottle. The EZ Caps seem to be holding pressure as well so I've been leaving them on till I'm ready to drink my soda. I'm keeping insulated glasses in the freezer, drinks, caps, bottles and a funnel in the fridge. When I fill the glass I immediately refill the bottle with the same kind of drink replace the same cap and recharge. This way I don't have to spend quite as much time cleaning bottles, caps and funnels. I would have given this product a solid five stars were it not for having to replace the seals in the caps.

These work well if you replace the washers with EZ Cap, Grolsch style washers as the supplied washers are too soft and have too large an internal diameter to seal with most plastic bottles.
If you do so, then these are an economical way to carbonate multiple bottles at whatever pressure you want. One cap per bottle for beer or if you use it for water, you can force carb at 30 psi, shake the bottle and then place a regular cap on and it's much cheaper than Sodastream.

Been using these for about 6 months to make soda water in 1 liter bottles. Instant gratification and much cheaper that a sodastream.
I have found that you need to be careful about the seating of the gaskets - they tend to shift and bunch. It would be nice to be able to purchase spare gaskets here.

I was thrilled to find an alternative to the ball lock screw-on cap version. However, be aware that this one doesn't seal with all bottles. Some won't seal at all and others need to be tightened beyond normal human ability (but are most homebrewers merely normal humans?).