Just in case anybody's not familiar with the ADAC, it's not a consumer body like Which, it's the largest German car breakdown company (equivalent to AA or RAC) - but they also do loads of car-related tests.
The ADAC used to have a pretty good reputation, but last year it came out that they were faking results in their own surveys, loads of resignations, breast-beating, etc.
I think the product tests are fairly reliable though. We've certainly always consulted them before buying tyres, bike helmets, etc.
Here's the test itself.
The seats are divided into different age groups. The 'grades' are on the far right - like German school grades, they go from 1,0 at the top to 6,0 at the very bottom - 5 and below is a fail. So the top grades go to the two Cybex models for babies under a year, and the Kiddy Phoenixfix for 1-4 yo. Shocking that the three models which failed were the most expensive.
There was a comment that a higher proportion of seats failed than would usually be expected.