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Bristol_Jonesey
No I'm pretty sure it was gone in X3, but it was definitely there in 8.5
 
So..... 8.5, X1 or X2 saw it's demise

I have the Pentagon DXi installed in Platinum.
 
The installer is definitely still there in the X3 installer.  I have 8.5, X1, X2, X3, & Platinum.  It's gone in Platinum.
 
I only put X3 and Platinum on my fresh Win 10 after clean installing.
 
Try re-running the X3 installer, select advanced install, and uncheck everything except the Pentagon DXi.  You should be good to go.