KotR do more damage but Eden can be used as many times you want in a battle and also be used as a 9999hp sheild. I didn,t think it worked to Quadra magic-KotR but i never got KotR so i don't know... but my friend got it and said they didn't work together.

KotR= 13x9999 while eden does at max 60.000 damage.

As for the combo... Zells Duell can be more powerful than Renzokuken.