i ride the rollers mon-friday every week. its the only time i can ride (school starts at 8, and it ends at 3:30, so by the time im home i would have an hour of daylight and my parents are big on the whole night riding thing). i like them becuase i can just focus on a zone, but riding outdoors is better, and even if you power histogram isnt prefect (lets say you spend 45 mins in z1 1.5 hours z2 and 45 minutes of z3 for a 3 hour ride), the power discrepancy can just be that you went under z2 power by 5 watts or so ( i like to look at the individual watt breakdown not the zone) and went over by 5 every now and again. For me i just try to average 230-250 on my z2 rides (i like the middle of z2 more than the tippy top of z2), and make sure im pedaling all the time (once again not perfect, but if i pedal for 98% of a 4 hour ride im happy).


edit: I also am big on z3/z4 intervals at the end of my rides, and long z3 rides later in the winter say around late december. 3 hours at .85, while pedaling at 70 rpms is tough, but it builds so much power!