I just got a pair of these, and wanted to post some brief impressions.

Build quality is very good, particularly for a sub-$100 product. Packaging is great, and matches the photos provided by other.

Sonics: Slightly bright, or maybe a better way of saying this is slightly lacking in bass. I have been using these on the train with an iPhone 7. I finally broke down and selected the Bass Boost EQ. With this on, and the volume increased some to compensate, they are perfectly adequate and sound quite good. Material I have been listening to is mostly shoegaze (Curve, Catherine Wheel), as well as some Radiohead, and Peter Gabriel.

Fit: I tried the included Comply tips, but felt they accentuated the brightness too much, so went back to the factory installed tips. These seem perfectly adequate for my use. I haven't tried the other supplied tips yet, but might this weekend. These seem to isolate well, both for incoming as well as sound bleed to people seated next to me. Since I am normally on a "Quiet Car", this was an issue with the Apple dual driver ear pods I had been using.

Conclusion: I am quite satisfied with these. I may have to listen to the Neo 12 Classics as well and see what I think of those.

The Rotel RCD-991 was the successor to the previous flagship RCD-990 player. The 991 differed mostly in the transport used; the previous 990 uses a Philips CDM-9 Pro, whereas the 991 uses a Sony KSS-213. The Philips used in the 990 is perhaps a better sounding pickup, but suffered from reliability and availability problems (try finding one now).
 
The player operates smoothly and quietly. All function are accessible via the front panel; most can also be accessed via the remote control. It also offers the ability to adjust dither; a feature that I am not too familiar with. Internally, the player is comprised of a single PCB which is well laid out and of very high quality. Blackgate and Nichicon Muse caps are used prevalently; the Blackgates around the DACs, and the Muse caps in the output stage.
 
The biggest gains in modification to this player involve the output stage (I/V). Stock opamps used include the NE5534 for the I/V section, NE5532 for the anti-aliasing filter, and OPA2604s for the buffer/single-ended to balanced conversion. A choice of either single-ended (RCA) or balanced (XLR) outputs is offered. Modifications to my unit include THS4031s for the I/V stage, and AD8599 for the buffer stage. These resulted in much better sound, though the unit is quite good in stock form as well.
 
Rotel offered a tweaked version of this player in the RCD-991AE. All modifications to this that I am aware of were in the output stage.