Sharing my findings:
I bought two of these - one for me and for my best friend. I, too, had a bunch of problems, as people highlighted. The first issue I had was my SD card not being detected. Working solution was to replace the cards with Sandisk brand. The next issue I had was constant graphical issues. At first, I thought it was related to if I flash to ROM/RAM; however, after further testing, I found that it is actually luck-of-the-draw: if I flash repeatedly, each result is different. To make matters worse, of the CD roms, only 2020 Baseball (CD) would work. Finally, upon looking into the file directory, I found a BUP folder which had a file in it - it was actually a file from one of the games that had crashed, but it wasn't the last game I played. I deleted it, and now, everything is working consistently! I have been monitoring for the past couple days and it works flawlessly - CD and roms.
I made duplicate SD cards, but I have yet to try the second NeoSD to confirm if everything is working the same.