I have 2 nero 5s I switched from the mp40s bc my tank is a corner bow so the ability to change the angle of the powerhead was great. It is also slimmer than the mp40 which is nice. I bought 2 guards bc I was worried about fish also, bc of all the reports, honestly the guards just collect algae... I removed them a month and a half ago. And I have no issues or concerns about my fish any more than with the mp40s. I like them. I just wish they would fix the software for the random mode bc you cant put them in anti sync. And also when you put it on the fastest changing speed it only changes once every 60 seconds. Where the mps were able to anti sync and were truely a reef Crest where it didnt sit at one speed too long