First-past-the-post with top-up-seats

I have long thought that the least-worst type of electoral system would be a combination FPTP with top-up seats so that the final number of seats in Parliament are proportional to the votes cast (provided a party achieves a threshold of say, 5%).

Instead of top-up seats being allocated by party-list (which people tend to dislike), a party's top-up seats would be allocated to its unsuccessful candidates in order of how many votes they achieved personally.

I batted this back and forth with Neil Harding, and he discovered that they have exactly this system in the state elections in Baden-Württemberg in Germany. So it does exist, and it does work.