I own 3 bikes that have S&S couplers.

One was retro-fitted on an old frame, the other two are custom builds that I had the S&S couplers installed in during construction.

S&S couplers are a great system and work very well. I suppose they add a little weight to the bike but it is less than a half pound.

They make no difference to the ride of the bike at all, in fact they may stiffen the frame somewhat if anything.

If you have a bike that you would like to retrofit - there are a number of builders that do that work, pick the one closest , or most convenient for you.

As to airline charges. I have never been charged either over-weight or oversize charges with the S&S case. You will, assuming you have another piece of checked baggage, be charged the "2nd checked bag" charge. I have only ever been charged this when flying internally in the US.

I have not beenn charged at all for the S&S case flying internationally or within Canada.