the se series is the upgraded e series, but not sound wise, when comparing them it goes like this.
se110 = e2c
se210 = e3c
se310 = e4c
se420 = e5c
se530 = e500
now the new se series does carry supposedly improvements over the e series, for example the se310 is arguably a nicer design than the e4c, but apart from that the se310 offers a tuned bass port and the e4c doesnt.
the tuned bass port is a small hole in the armature housing and it improves bass response but not accuracy, ports dont improve accuracy, they just improve depth response. for this reason some will argue the e4c is tighter in the bass, but when bass is that minimal most prefer a little more bass as standard, the se310 offer this.
again the se210 is arguably a nicer set of phones than the e3c, both are single drivers with no bass port, its really down to what looks best to you, although the sound differences are not many, some people argue the e3c is better and some prefer the se210.