Before purchasing, I had two major concerns about purchasing an NVD
1. Would I mind a small FOV of 40 degrees?
2. Will the aesthetics of the star display bother me?
I found it challenging to clear both of these doubts just by reading online forums. An evening with NVD under the stars would solve my worries, but no one in my immediate or distant surroundings has such a device.
In the end, encouraged by the posts on this forum, I decided to buy 'blindly', the price is ridiculous :-), but it turned out to be my best investment in this hobby of ours!
So, for those who may be in a similar situation:
1. Small FOV?
I really enjoy the relatively large FOV of my Morpheus, Pentax, and even Panoptic eyepieces. I was truly afraid that those 40 degrees would be too little for me. What can I say, never but never does the view through the NVD seem cramped to me. I can't explain why, probably a combination of the amount of information in those 40 degrees and the long eye relief. Simply, for me personally, those 40 degrees are not a problem at all.
The NVD FOV has become so natural to me that recently I started using my Baader ortho eyepieces for DSO as well :-)
2. Aesthetics of the view compared to glass eyepiece?
Before buying, I saw on internet forums a lot of nice (processed) photos through NVD eyepieces, but also a lot of terribly bad photos and ugly green flashing videos :-) of NVDs in action. I wasn't sure what to expect.
When I inserted my new NVD (OVNI-M 2100) into the diagonal, at first glance, the aesthetics of the view were truly worse, but after a little use, I would even say that it is not so bad as different compared to glass.
So, first of all, NVD does not have the colors of the stars, but it also does not have the pinpoint brilliance and dynamics of the view through a quality glass eyepiece.
On the other hand, when in the 4-inch achromat, in bortle7, you see a resolved small M79 globular cluster at only 16 degrees ALT through the haze of the atmosphere, then the aesthetics somehow fade into the background. In my opinion, the best description of the image would be that the aesthetic is similar to those invented scientific photographic plates with black stars on a white background.
When I start observing the stars through the NVD, somehow I put myself in that beautiful-ugly 'scientific' mode where what you see is more important, not whether the object you see sparkles beautifully :-). And what is most important in my opinion, I really enjoy that presentation, even though it is somewhat worse. When I'm hungry for beauty, I put in Pan35 and turn to Pleiades or DoubleCluster.
One more thing to add, the overall image quality is much better in prime focus compared to afocal, it is also slightly better in the APO telescope than in achromat, so that should be kept in mind. All of this refers primarily to the aesthetics of the star display, the nebulae are phenomenal through NVD.
Of course YMMV.
Clear skies to all!