You are getting conflicting advice because you are unclear with
your question. The NT3 has a wide pic up pattern. It’s fine for
“indoor” use. So that answer is correct. But the NT3 must be
quite close to the actor. That makes it excellent for Voice Over
use, for example. Watch the video wynnep suggested.
http://www.youtube.com/watch?v=ETX_nBG9zvU
When the NT3 is very close to the speaker it sounds great. So if
by “indoor” mic you mean a mic the speaker will hold in their
hand a few inches from their mouth (like the woman sitting in the
chair) or put on a stand a few inches from their mouth (like the
woman in the studio) then that’s the mic for you. Watch the
video. Is this the way you will use the mic?
As soon as you move it out of frame it will sound like the
sequence in that video with the woman sitting and reading without
a mic close to her. A good shotgun mic will sound good from that
distance.
If you can afford two mics - a shotgun with a lobar pick up and a
vocal mic with a hypercardiod pick up then buy both of them. If
you cannot afford both, buy a shotgun mic.
Check out
THIS EXAMPLE What you will hear is a Sennheiser
shotgun mic used indoors. The first part has a lot of camera
movement - which means the boom op had to move the mic
around a lot. Something that couldn't be done with the NT3.
In the second part you see standard close ups. The mic was
above the actors, just out of frame. If you feel the audio isn't
good then the NT3 is your best choice. If it sounds okay to
you then you can try a shotgun mic.