I've owned both these heat sets for a while and I thought I jot down some impressions.
These two headphones are about the same price, are about as well built as each other, but the could not sound more different.
Sennheiser HD-210 I pick these up for under $15 online somewhere about 2-years ago and they've served me well as a basic "around the house" headphone.
They are forward sounding, have very good mid-range resolution, and are comfortable; however, they do get hot for extended listening, and are very thinnish in the bass category. If you like thumping bass-lines, look elsewhere.
JBL Reference 410 I bout these a few months back also for about $15, but haven't had the opportunity to listen to them thoroughly until recently.
The 410s are a solidly build, folding design, one that provides a very tight fit that is perhaps a bit too tight, and also a bit hot, I found them to be slightly uncomfortable, but they do create a tight seal, that lends itself to the heavy bass sound of the 410.
This headphone is all about the bass, bass is up front, solid, and omnipresent, mid-rage sadly is setback and muddy, which doesn't make for very pleasant listening in my book.