I would like to know if the other options on the market (ie; Stages SB20, Wahoo Kickr Bike) suffer from the same issue with ERG power fluctuations?
Maybe we are expecting smart bikes to do the impossible by changing resistance continuously whilst fighting against the riders power output so that the line on the graph is perfect?
I own a NG Atom and find intervals under 30 seconds a bit pointless unless I keep my power going through the pedals very smooth and consistent. There is a knack to it as you have to jump on the power just before the interval starts so that the bike has less adjustments to do, this is a lot easier to do at the beginning of a workout but not so much towards the end when you are hanging on for dear life!
On a positive note the resale figures for a NG Atom are crazy high at this point in time, I could move mine on for the cost of a brand new Stages SB20 or by adding a couple of hundred quid get a brand new Kickr Bike.
The Wattbike is a great bit of kit in my opinion, but I have nothing to compare it against.