A couple data points for you to consider before buying:
1. Burley has gotten out of the tandem business -- at least for the time being. While you would no longer be covered under any warranty (only extended to original buyer), if you need bottom bracket parts they should still be able to either provide or direct you to other sources who can provide the parts / service you might need.
2. Softride stopped beam production a while back and replacement beams are no longer available. If yours gets damaged for some reason, you'll need to find a replacement on your own.
3. The pivot bolts used on the beams are supposed to be replaced every 2 years / 5,000 miles; you'd want to contact Softride to see if they still have the Rear 101 Suspension Rebuild Kits or at least the pivot bolts for your particular Softride Beam.
4. If that Burley's beam has the Allsop name on it, be forewarned there were some quality issues that didn't get fully resolved until Softride acquired the beams.
5. There were two different model beams. The Model #530 (aka the 392) was the the stiffest model offered and is what builders like Co-Motion installed on stock Cappuccinos unless a customer specified the more lively, lightweight model #510. There is also a model #520 mid-weight model. The lightweight model #510 was only approved for a maximum rider weight of 200 lbs, but my memory is a bit vague on weight limits for the other beam; however, it's included on the information label on the underside of each beam.
In addition to important points noted by the geek a parenthetical
observation based on watching a local singleton softride: the
rider bounces up and down a good bit which messes a bit with
your cadence, resonance can occur with certain cadences at
lower cadence RPM than most bikes (resonance means rider
starts bouncing up and down at some point-usually at cadences
in the 100rpm + range). Since stoking means exposure to some
considerable road shock softride has its attraction, but can be
bouncy with longer wavelength undulations.
While it's recommended that the pivot bolt be replaced @ 5K miles, know several folks who put on many more miles and have not replaced the bolt ever.
Do not personally know of any beams ever failing.
While stoker observed a bit of excessive bounce at very high rpm, that was easily resolved by shifting down to the next smaller cog.
We regarded the beamer as the best suspension system for most tandems.
Pedal on TWOgether!
Rudy and Kay/zonatandem
I didn't distinguish between the shock absorption bounce which is the whole
point of having the soft ride and the bounce from energetic pedaling, which
at certain cadences can result in the noted 'resonance' where the bounce
exagerates. On a DF or the tandem this occurs about 105-110 rpm cadence.