I'm sorry that I'm just getting to this now after a crazy day yesterday.  I'm glad that you like the Concept 2s.  I saw someone rowing on one at a hotel fitness club this winter with totally the wrong form.  I'm glad that you know about proper technique.  My only gripe with concept 2 is that it isn't a boat.  

So good for you for doing the workouts.  It's good to mix the longer pieces up with some sprints.  Do you use the workout plans on the website?  I had one erging coach that used them and one that used her own.

The other great thing about rowing and erging is that they're good for bone health.  I've been diagnosed with bone issues and started to freak when the doctor told me.  "But rowing starts in another month!" I whined.  But she said it was great for bone health because it's considered a weight bearing exercise.  So she told me to row as much as possible.  Not a hardship here.