Sometimes what you think is a good shot really isn't when you study it. And I found out the hard way a 3-D target is harder to hit than a spot target if you have never tried it before. Especially at longer distances. They are a great learning tool if you can get one to play with. Some have the outline of the bones instead of scoring rings, those are the ones I like.
I agree with Paul here. When I shoot outsideall I use is a 3D target. If I could get my local range to let me I would bring it indoors as well but this little range does not allow that.....yet (I'm still working on them) I feel it's better practice than a target. It helps with finding the kill zone quicker because well...it's a deer your shooting at and not a circle. Now I must add that all I do is hunt and therefore have no use for targets other than practice.
To answer your question with a hunting perspective only, 3" groups at 25yds isfine. The key is consistancy, if you can do that consistantly then if I were you I would go into the woods with all the confidence in the world in my ability to make a clean kill at that range and even further.