Fan not needed. "Sufficiently kick your ass" is a correct assessment
As a former competitive rider just getting back into it for fun, I am as happy as you could hope to be with rollers. I used the large diameter Kreitlers in the 80's and I recall needing the wind-load simulator fan in order to really work. NOT SO with these. The rollers alone provide an ample workout for me. I estimate these provide 75% of the normal resistance you experience outside for a given gear on a flat road with no wind. It would be interesting to know if Kreitler has a more accurate equivilency.