You're welcome! Thanks for the 5-star "rating"!
It would depend on the amount of turnover you're looking for. I had four Hydor 425gph (constant "on") before I replaced them with two Nero's. That was 1700gph of flow with no randomness, which equaled about 26x turnover just on the powerheads. With the Nero's as I currently have them set (I'm still playing with them a bit), when both pumps are at their approximate peak (1550gph), I'm at 3100gph or 47x turnover. I have a mixed reef but the right side of my tank is dominated by 3 large anemones (splits of one-another). The other corals (zoas, mushrooms, a few LPS) seem to be happy and the fish seem to ride the currents... looks like fun!
Anyway, it would be a personal decision based on the dimensions of your tank and what kind of flow/turnover you're looking for. Two at the minimum setting would be 1800gph or 45x turnover... that's near what I have on my 65g at it's "peak" - when both coincidentally hit the 30% mark at the same time (I do not employ the parent/child feature - I intentionally want it to be as random as possible). However, if you set them both on their lowest constantly, then you wouldn't be using all the features... you might as well buy cheaper AC pumps if you're going to do that. However, you could perhaps just buy one Nero, and then have a second AC pump mounted elsewhere on a constant mode/backup. That way you could take advantage of the AI app, have full control of both the lights and the flow in your tank, and save a few dollars in the process.
Hope that helps!