We get 6,000 miles off a drive chain by keeping it clean/lubricated. Much more mileage yet on the cross over chain as 'stretch' is not critical.
The extra $$ on the W'man chains is questionable altough we have never used them.
If you live in a wet climate and don't do much chain maintenance, the stainless steel may be worth it as it shoiuld not rust, however it'll still wear out.
Personal philosophy: Chains and tires are products that tend to have mythical qualities in that different cyclists will quite often honestly report both incredibly good and pathetically bad performance from an identical brand and model of chain or tire. The answer to the logical question of "how can that be" is quite simple: different riders (and tandem teams) have different expectations and place different demands on their equipment. Hence the ubiquitous, "Your Results May Vary" is always an appropo disclaimer for any post on bicycle products, tires and chains in particular.
I've run them on my personal road bike (Campy 9spd), but not on the tandems; a bit noisy but then again I use a hot-melt paraffin wax bath for chain lubrication which does tend to result in exceptionally clean drivetrains but a tad more chain noise. I also have a miniature, stainless steel Wipperman chain around my right wrist. It has endured many hot and sweaty adventures and has yet to ever need any lubrication nor show any signs of rust, corrosion or wear!
Less I digress, back to your question...
Short Answer: I think there are better choices for tandems running 9 speed than the Wipperman. Moreover, while more durable, according to some test results, they are not necessarily as "strong" as some of the other more popular chains. Thus, while a great choice for a personal bike, they may not necessarily be suitable for the rigors of tandem use. That said, if you can find them on sale, like nice looking chains, and like to keep your drivetrain clean, and are a finese shifter, give 'em and try and see how they work for you. If they run smoothly, shift well, and seem to give you more mileage than other chains that you've used, perhaps they would be worth the extra $$. However, I would be sure to carry a chain tool & spare Conex or SuperLink in the event that you discover the threshold of the Wipperman's ultimate strength.
Long Answer: For our road tandems, I run either SRAM PC-69 or better or the mid to high-end Shimano chains. As to which brand & model I have on a tandem at a given moment, it depends. I buy the better chains whenever I find them on sale for around $18 - $24/ea. The Shimano chains and cassettes are about the best on the market... no kidding. I say this having argued in defense of SRAM's chains which ARE good chains. However, Shimano upped the ante years ago when it developed the IG and HG technology which makes for easier shifting on off-road use and for road riders who have a tendency to shift late on climbs (e.g., under load). If you're a finese rider who spins a high cadance and who knows how to get buttery-smooth upshifts into the big chainring the SRAM are just fine and dandy. In fact, a finese rider doesn't even need ramped and pinned chainrings. But, finese riders are far and few between these days as most cyclists have either fully converted to or started out using integrated indexed shifting systems both on their road and off-road bikes. Thus, Shimano definitely has an engineering edge on other chains since most bikes (including my campy-equipped road bikes) use Shimano cassettes. NOTE: Campy is now offering it's wheelsets with Shimano-cassette compatible hubs. Another thing to keep in mind is that the chains sold by the various different manufacturers all vary in width and Shimano are about the most narrow of the bunch. Thus, if you have a finicky rear derailleur/cassette combintion that "chatters" in a few cogs using a SRAM or Campy 9 speed chain you might be interested in trying a Shimano 7701 (XTR/DuraAce) model to see if that doesn't reduce the chatter.
One argument against the Shimano chains is the stupid, one-time use rivets. FWIW, I don't use the rivets and, instead, use SuperLink's on all of our chains. These suckers are the best little resuseable chain links on the market.
How Long To They Last? Not long. Chains are best treated as consumables like tires; they perform a basic function and have a finite life. Discard them once they become marginal because left to wear too long they have the ability to do far more damage to more expensive parts (cassettes and chainrings).
New & Improved or Hype? Chains are somewhat akin to gasoline; all brands are basically performing the same function and are differentiated mostly by additives that the marketing departments hype in the hope that you'll chose one brand over another. At the end of the day, how you use and maintain your equipment is what really determines how well either of the products (gasoline or chains) will perform.
Put into practice, here are some practical thoughts for use in guiding your chain purchasing decision:
1. If you never clean your chain or drivetrain then you should buy the least expensive chain from KMC, Shimano, or SRAM, slather a wet-lube on it and merely discard it once it wears out enough to show .50 on a Park Chainchecker II or "stretches" beyond 1/16" using a Ruler.
2. If you're the average cyclist who cleans the drivetrain every once and while, do the same thing as 1, above, with cleanings and recognize that you'll get a little bit longer life from your chains.
3. If you're an equipment freak who's meticulous about keeping your bike and drivetrain clean and love the look of shiny chains, you can spend the extra money and get the higher-grade chains and you'll get even more miles out of them than the average cyclist who occasionally cleans their chain. But, they'll look great!!!
I have the stainless Wipperman on a standard bike. I like the ability to use a dry lube like Prolink without rust. Is it worth the $$? Prob not. Thinking about getting one for wifey.
I have been using Prolink on my mountain bike with a SRAM PC68 for the last couple of months. I mainly ride the bike to class and it sits outside in rain, snow, salt, etc for many hours a day. I think I average reapplying the Prolink every 2 weeks, sometimes every week, sometimes once a month. So far the chain looks like new with no rust and I think the Prolink works better in wet conditions than most wet lubes. I wouldn't give all the credit to the Wipperman for not having rust. I was considering trying a Wipperman, but I think I am just going to stick with chains like the SRAM PC99.