Pros and cons of digital camera based negative/positive digitizing from my experience:
+ Cost: using existing camera either with tripod or BEEON and photographing the 35 mm film with macro lens with keeping the sensor parallel to the film plane let's you use existing gear. Dedicated film scanners start around $350 (Plustek 35 mm scanners) and go around and above $1K for larger film formats. Scanners like the Epson V750 to 850 give the best flexibility in regard to formats.
+ I am not using Nikon gear, but reading about the digitizing adapter, it would allow to record RAW files of the film and does some sort of in-camera white balance adjustment.
- Both methods - with tripod/BEEON or digitzing adapter only allow simple digitizing for 35 mm film format. For larger film formats, PP with photo merging is required (only possible with tripod/BEEON method and not with the Nikon adapter) which can be more time consuming than scanning with a dedicated scanner.
- The tripod/BEEON method does not allow the application of white balance control - which is IMO essential for color negatives to achieve good control of the color representation.
- Speed: Slowest digitizing process by doing it with a digital camera especially if larger film formats need to be digitized.
- Flat film: Dedicated film scanners use film holders which flatten and fix negatives to scan. Best to use with the digital camera method is an enlarger based clamp, but it also takes time to load each frame separately by fixing and moving it in place.
Both methods - digitizing with digital camera or with dedicated scanner - work. It often depends on the volume of film frames to be digitized. For larger volumes, a scanner is a must IMO.