I have always sown in pots to plant out early March, this year I did not have enough to finish a row so I finished the row by pushing in some seeds of the same variety direct into the ground.
The difference between the two was remarkable, the direct sown seeds grew taller, more lush, the pods were larger and more uniform. They even had less black fly and chocolate spot, and were only about 2 weeks behind the others.
I am going to keep the seed from the direct sown beans to sow next year, not bothering with pots, but sow direct in March.