The E3 is Bauer's budget entry into the Nexus line for recreational players, while the E4 targets performance players wanting better construction and blade tech at a mid-range price.
Verdict: Pick the E3 if you're a recreational player on a tight budget who just wants the Nexus mid-kick feel without extras. Pick the E4 if you're a developing or intermediate player willing to spend $30 more for meaningfully better blade feel, lighter weight, and more flex options. The E4's upgrades justify the price difference for anyone playing regularly.
Bauer
Nexus E3
Bauer
Nexus E4