If RevAir isn’t straightening your hair as effectively as you had expected, it may be because you are not getting enough tension. Try using the highest Reverse-Air Speed and Heat level that proved sufficient for you when initially testing. To tolerate high speeds, some long hair types need only a trim to Rev tangle free.
Still, while RevAir straightens all hair types, some will stubbornly hold on to a bit of their natural texture to some degree, particularly types of curly and coily hair. In this case, flat irons may still be needed to achieve the look you want. However, you are likely to find that they are needed for much less time than had you not used RevAir first.