We currently have over 13,000 miles on our Zona full carbon fiber custom tandem.
In our opinion/experience, a properly built c/f tandem is the best ride for us.
Yes, we've owned other custom tandems that, in their day, were the cat's meow. However, materials/needs/designs do change. Have ridden 30+ brands/models of tandems in our 31+ years of riding TWOgether (Yes, have ridden 'tanas and Calfee, and the Calfee really turned us on to owning c/!).
Seems sad/odd that you ordered a new tandem in May and want to replace it in September?!