Nikkyo ura is one of the techniques which has its pros and cons depending on what you expect from it at any given time.
Personally I love to go into ikkyo, lock the arm of uke on my leg - and then set up ura from there. [control, control, control... at each point there is no way for you to do anything - its really fun this way as it gives you the most control and you can play with uke like a puppet.]
Of course there is the non-lock version where you basically start off with nikkyo, but I find it time consuming to be practical... not saying that it cant be mastered that way, but fast paced is trickier this way from what I have experienced.
Basically I look at ikkyo as the base for all the pinning techniques for the most part [well, to be fair - ikkyo, nikkyo, sankyo, as yonkyo, gokyo, and rokkyo have a bit of a different swing to it... for me rokkyo and kotegaeshi ura go nicely together - if one isn't working the other is a natural back up in a quick situation.]
Anyway... hope you find a way that works for you and you enjoy.