How to align face with another face which extension is the best for that?
alignface.skp (288.9 KB)
Hi there !
I don’t know about the extension you could use…
But there is a simple way you can do this with native inferencing !
That’s how (I’ll try to explain clearly) 
On your curve object (in the group) :
1.Draw a line more or less parallel to a axe on the under side (the flat face underneath)
2.Then you can draw the perpendicular line using inferencing (make sure the two lines are on the face)
Then on the model (meaning out of the group) :
-You can rotate the object around the blue axis aligning one of the two lines to one of the axis.
-Then you can rotate the object around one of the lines to align the other line to the according axis.
-Finally, you can rotate the object around the other line to align the first one to the according axis.
Back in the object :
-You can delete the two line you used for the alignment !
You’re done !
It may seem tedious, but it actually take no time at all when you know what you’re doing ! 
Hope I have been clear enough, and helpful !
If not, here’s your file … aligned !!
alignface.skp (291.4 KB)
