how reliable?

I've owned two; a 2011 and now a 2016. My 2011 was virtually trouble-free for the four years I owned it. It did have a bit of an oil consumption problem, but that was a known issue for the early model years. By 2013, that issue was corrected and no longer a concern. Either way, the oil consumption issue was not that bad on my car, so I never brought it back to the dealer to have it fixed. My 2016 has been 100% perfect so far, but it's only a few months old. I doubt it will be any less reliable than my 2011.

We have a 2014 S5 convertible that has been trouble - free. Knock wood since it only has 10000 miles, but so far so good.

We bought a 2013 A5 cabriolet Boxing Day 2015. Zero problems. We had it serviced once at the dealership free of charge because the warranty included free maintenance for five years. We have put over 10,000 kilometres on it commuting to work and visiting my mother-in-law (800 km round trip). Nothing leaks, drips or rattles in the eight months we have owned it.