I've used my NB4 since July 2020. Several receivers for RC-auto and robots updated successfully: FGr4 v.2 (2 pcs), FGr4P, FTr10. Everything works quite well.
For now, I fixed a couple receivers(FGr4, FTr10) and NB4 itself to get more RF-power (about +7 db up). Just Great - more reliable connection, remote and telemetry distance!

Can tell you about via personal message, if anyone interested.
Suppose, Flysky NB4 - one of the best for RC-auto (IMHO)!