There is an article published on the Sound Devices website that answers your exact question. The 7-series outperforms the 552 in terms of the dynamic range (114 dB compared to 103dB respectively), which is more important when dealing with low-level recordings. 7-series recorders are also more flexible in terms of input routing. But the 552 is an excellent production mixer. As with any Sound Devices unit that I have used, the 552 is very intuitive so usability shouldn't pose you any problems.