They seem to be well regarded race bikes. For example, the Orange Tandem is a Duratec.
Tandem Road and Track Racing in Australia - Orange Tandem Racing Team There are a few other Duratec tandems racing in Australia.
From memory (fallible) the back end is restricted to 130mm OLD so a wide range of wheels are available, but are less suitable for heavy teams or touring.
Cheers,
Cameron