Is it safe to use Windows insider to upgrade my Nokia Lumia 640 to Windows 10 preview build?

[skt_diaz]

joined insider preview just to see how many bugs the os actually has. lock screen does take some time to unlock and calender shows wrong birthdays on the live tile. does anyone else have the lockscreen issue?i did reset my device after the update, still there's lag in the lockscreen and some other areas.