These are essentially what the Hedman elite series comes with stock.
The little bit I've had my setup together and running, they seem great.
I too wondered about the flex/seal issue, but I don't believe these are a solution to that. If there is movement at the connector (as I see it) there is enough room for leaks. (and noise, and failure, and so on)
I know that when most people here talk about flex they really mean it, but I'll trumpet the stock exhaust system 'till the cows come home...they are solidly mounted, and very rigid, except the rubber isolators at each point. I think keeping the exhaust solid is a better solution than trying joints that can move. I can't stand the cheap stuff most aftermarket junk is hung with. Plumbers strapping is NOT up to the task.
Perhaps some of the tubing that is actually flexible in a strategic location would be a good compromise, but I'm unsure if most of what you see aftermarket remains flexible, or if you'd have to go more towards the newer OEM flexible stuff.
For disconnects they are certainly quite handy. For that price though, (and I did look at those before I bought my headers) I'd probably see if anyone offers a header set that meets your criteria with those sockets included.