While Nd7 seems inferior because of the weak bishop, this was never tested in the only instance this move was played at master level, between Rustam Kasimdzhanov and Mikhael Mchedlishvili in the European Clubs Cup (Men) in 2003. (That game quickly transposed back to a main line, continuing: 6...Nd7 7. Nf3 h6 8. h5 Bh7 9. Bd3 Bxd3 10. Qxd3 e6 11. Bf4 Ngf6 12. O-O-O Be7 13. Kb1 O-O 14. Ne4 Qa5 15. g4 Nxg4 16. Ne5 Ndxe5 17. dxe5 Rad8 18. Qh3 Qb4 19. Rdg1 Qxe4 20. Rxg4 Qh7 21. Rhg1 Kh8 22. Qg3 Rg8 23. Be3 a6 24. a3 Rd7 25. Qg2 Rd5 26. Qg3 Rd7 27. Qg2 Rd5 28. Qg3 1/2-1/2.)
It may appear at first that White can trap the bishop, but this is not the case after 7. h5 Bf5 8. Nxf5 Qa5+! +=. However, White can do this anyway and get the bishop pair and light-square control.