Thanks for the replies everyone. I hadn't thought of having two S&S cases and the hassles that a large full-size tandem box would present once it's on the ground. In summary I believe there's pros and cons to each system....
Safecase vs. two S&S couplers. There would be baggage fees associated with a Safecase but it seems a Safecase offers better bike protection with the use of shaped foam. No fees on the two S&S cases provided they are less than 10" thick. To my knowledge there's no room in either for a rack.
Safecase vs. full-sized tandem box and no couplers. Same cost to fly either but the full-size tandem box is a nightmare once it's on the ground. It seems that a full-sized tandem box offers very good bike protection. So the bike will get there just fine under either option.
Two S&S cases vs. full-sized tandem box. The coupler option would cost almost $3,000 more once taxes are added. The same for the Safecase. A carboard tandem box is free...it comes with one on my new tandem. I may get several uses out of it by strapping it down securely. There's room inside the tandem box for a rack, helmets, shoes, etc.
I do like the idea of couplers however $3,000 is a lot of money and it will take many trips to recoup the investment. If the cost is more reasonable like $1,500 then it would be a no-brainer.
It seems to me that many tandems are flown not having couplers so I do think it's a viable alternative to having couplers, provided that the trip has ground support to handle a large tandem box. It's likely that I won't do any 'credit card' type touring on my own in the foreseeable future.
Last edited by pdlpsher; 04-06-17 at 07:45 AM.