So for a while I've been using the modded eBay iPod - which is FINE, but the build quality was kind of shotty. I kept reading great praise about the 5.5 generation iPod as the pinnacle of sound and mod-ability so I finally caved and got one. While there are some aspects I really like about it, I'm overall a bit disappointed (most of it on me).
I got a 512 GB model from PiratePTiPods on Etsy and the build was fantastic. My issues with the 5.5 generation as opposed to the 7th generation:
PROS:

Also, I couldn't really tell a difference between the 5th and 7th generation sound, but I only did minor test and didn't really expect a night and day difference.
I got a 512 GB model from PiratePTiPods on Etsy and the build was fantastic. My issues with the 5.5 generation as opposed to the 7th generation:
PROS:
- I really like the white-faceplate with black click wheel contrast.
- The click wheel itelf is more click-y than the 6th/7th generation.
- Flat album art with more 3D progress bar on now playing.
- Scrolling and navigating menus are snappier.
- The 5.5 generation has some hiss with my IEMs that isn't present on the 7th generation (Moondrop Kato)
- While I knew the 5th generation had simpler software, I think the little accents such as listing the number of songs in a playlist or the artist of albums/songs in a playlist is nice and helps identify items when you have many songs of the same name.
- Slower in some regards than 7th generation. Outside of scrolling, booting up the device, waking from sleep, and even changing songs can be slower than the 7th generation. Sometimes album art is missing for a few seconds which never happens on my 7th generation.
- No playlist folders - this is on me for not researching enough, but I never thought to check. Playlists are my primary way of listening to music and the 5th generation just shows ALL playlists in a list and doesn't respect the folder structure from iTunes whereas the 7th generation does.
- Stutter on playback with some lossless tracks. Some of my music (24-bit ALAC from Bandcamp) stutters on this iPod to the point where I can't listen to it and while it's playing navigation lags tremendously. I know it's because the iPod is sampling the 24-bit down to 16-bit, and while I'm not an audiophile - I don't want to convert my library on each sync. The 7th generation has no issue playing any of my files with no slowdowns.
Also, I couldn't really tell a difference between the 5th and 7th generation sound, but I only did minor test and didn't really expect a night and day difference.