I recently viewed a couple videos comparing different pumps, including the video above in post #49 from Spike. One video
did a sound comparison of the March (didn't catch the specific model, side inlet) and the Riptide. The Riptide is quieter by my ear, no instrument measurements were made. Another video
used a phone app to measure decibels, so while perhaps not a dedicated instrument, there were significant differences in measurement between a Chugger (90dB), a March (88dB) and a Riptide(72dB). The March and Chugger were about the same, the sounds were different in composition mainly to me. The Riptide did sound quieter than both and was 16dB less than the March and 18 dB less than the Chugger. I will point out that the tester appears to have a new Riptide vs his current March as it is mentioned to have been used as well as probably still missing its thrust washer. He's very upfront though and the comparisons are pretty reasonable.
Spike doesn't run the pumps in a sound test in their video above, they present their data in a figure. And having watched their video, I got the impression that their engineers put a lot of time into designing the pump head for flow and so I suspect that they at least used decent instruments to measure sound as well. Their results for the March 815 and Riptide are so close (0.5 dB), I have to wonder if some of these other video comparisons (Non-Spike) are seeing differences because of older March pumps vs. new Blichmanns. I am also going to note that Blichmann advertises the Riptide at 50dB.
Best comparison for 50 dB I could find is moderate rainfall, with 60 dB being normal conversation.
I wasn't able to brew on Sunday, so only brewed once this weekend. I did make it a point to note the difference between one and two pumps being on and that is significant enough to turn up the music volume some.
And as I said, I watched Spike's video. The bleeder valve design on the Flow is likely superior. They note that it is probably more important to have a solid column of liquid on the in side for priming which I have also observed in practice. I have my bleeder valves on my March on the in side myself. You would need at least a tee and a ball valve, I recommend a barb fitting as well and you may need at least one nipple ~$15-$25. I think they are likely on the right track with the center inlet, March pumps that differ in the pump head only (center vs side inlets) do have different rates with the center having slightly better stats. The Riptide's valve placement allegedly interferes with flow according to Spike as well. I think the Spike engineers have found that the integral valve may affect max flow different perhaps than a ball valve on the out. It seems to be what they are implying anyway. I agree with the Spike spokespeople in the video that typically there is a valve on the in ports of most typical brewing vessels that allow for easier flow manipulation as you can see inside the vessel without stooping. I use a valve on my BK whirlpool port and that's the port I use to transfer from my MT when sparging to throttle flow. I do however have a valve on the out of the pump as well which I use at different times such as controlling the sparge water flow into the MT and for throttling flow into the plate chiller for maximizing cooling and oxygenation. The out valve on the pump also makes hose transfer easier in my opinion. A 1/2" SS valve is about $10-$15 and you can pay more if you want to.