It looks like the "Starrschlepp" (rigid tow) tested by the german DFS. There the connection isn't
(wasn't) really rigid, but there was a kind of ball joint allowing for limited independent motions of
both aircraft. Tests are said to have been very successful, wit a considerable reduction of workload
for the glider pilot.
The advantage probably was, that with such a glider, the tow aircraft could transport oversized
cargo without many modifications, return to base, when the glider was just about to be unloaded
(or still in the air !) and so achieve a better "transport frequency"/efficiency.