A friend here had one installed. Came in in 3 or 4 parts, went together fairly easily (installed by the manufacturer's installer crew).
But they divorced after less than a year, so I couldn't tell you how well they stand up over time. My only worry would be separation at the joints, and that would only be a real problem if the foundation weren't solid.
Flexibility is honestly about par with what you'd find in new construction "estates" where a builder, again, has half a dozen styles that you can pick from, and customise lightly. And that's all they'll build to keep a certain uniformity to the section (read neighbouthood).
Most manufacturers will accept some light modification to their pre-plans, provided it doesn't involve structural, heating, or plumbing. Provided you're not in any great hurry.