In Europe, Latam, the merger of TAM and LAN airlines from South-America, is a relatively unknown member of the OneWorld alliance. It is well known among aviation enthusiasts, though, because it flies a short-haul intra-European route with a wide-body plane, the Boeing 787 Dreamliner. That plane is known for its comfortable atmosphere, a higher cabin pressure and higher humidity.
Apart from that, because the route is only flown once a day each way, the tickets are often sold against incredibly low fares. My wife and I just flew over to Madrid for 152 euro return - in business class. You get a lot of bang for the buck: priority check-in and security (not in Madrid), lounge access, priority boarding some 45 minutes before departure, and of course a very nice 2,5 hour flight including catering.
The business class cabin consists of five rows in a 2-2-2 layout. This is ideal if travelling as a pair, less so if you're flying as an individual. The seats turn into flat beds - however I'd rather stay awake on such a short flight. For those connecting from South America, this will be different: after the long haul leg from there, they will probably want to catch a few hours of sleep on their way to Frankfurt.
Latam provides a limited catering on the short flights; there is no choice for a main, only for a desert (which are delicious, by the way). The 'main course' consisted of a lovely cold cuts platter on the FRA-MAD flight and a rather meagre brie-turkey sandwich on the reverse leg. That said, food presentation is much, much better than on regular intra-European business class so there is no reason whatsoever to complain.
Personnel is generally friendly and speaks English well. They respond very quickly to calls made after the meal service. All in all, for those enjoying the experience, including lounge access 152 euro buys you 10 hours of 'quality time', which is truly amazing value. If you credit the tier points and miles to British Airways Executive Club, the return tickets also earns you 80 tier points and some 2,000 avios, worth some 20 euro.
You can find availability either by searching on the latam.com website or on matrix.itasoftware.com, where you can do a 30 day window search for business class flights between FRA and MAD. I would recommend you to book directly via latam.com (slightly more expensive at 168 euro) but if you like to take the risk of booking via a discounter OTA this will save you some additional 16 to 20 euro depending on the means of payment.