Jwscud: EPR does have one quirky advantage.
Say with a 4-eng aircraft the final approach power was 1.25 EPR This equates to a 4 x .25 increment ie. +1 therefore a 3-eng approach would require +1/3 ie. 1.33 EPR for final.
2-eng aircraft. 1.25 EPR would require 1.5 EPR for approach.
Simples!! It relates directly to thrust whereas N1 is not linear wrt thrust.