Never flown the real world BJ400 but I have a lot of experience on the X. The ES model handles differently from the real thing but that's not so unusual in FS.
What bugs me is that the devs have made no effort to replicate the auto flight control sytem - it's the same as the default Learjet

. I wanted to use this to practse for my next renewal, so it looks as though I have wasted $27.
There again, these devs can't even run a web site properly, so perhaps I shouldn't have expected so much from the add-on.