If you have an Apex and want to stay in the Neptune ecosystem then the Cor is a solid choice if it meets your flow needs. I have three Cor pumps. One since they launched to the public, one a couple months after, and the Cor 20 a little over 3 months. No issues with any of them. I can only compare it to Jeabo DCT 15000 which didn't make it through my tanks lead check before coming apart at the pumps outlet neck and body.
The Jeabo was quiet as noted above, moved a lot of water, but the build quality was lacking and felt like it was made out of the thin plastic you would find holding a Hostess Cupcake. The Cor 15 and 20 is thick, solid, built like a Ford F150. Really, it seems like a routed out solid piece of plastic through and through. Connected to Apex the Cor 15 will save you an outlet on the energy bar. The Cor 20 required a dedicated power supply for the extra flow and power. One Cor 15 is running my skimmer, the other is on the return connected to a 1" sea swirl. The Cor 20 is also on a 1" return line again on a 1" sea swirl but on the longer plumbing run while also being plugged into the wall rather than the energy bar or 1 link.
All in all they are good pumps. I was originally looking at the Vectra's but at the time the L or M1 was having a lot of troubles. While their support is top notch and everyone I know who had issues (one fella had 4 go bad on him) had great support and replacements. So while there was a issue, it was noted, and addressed via a update and they stood by their product. However, at the time the Cor started to get released and so I went with them. All in all I'm pretty happy. I used the Apex and a virtual outlet, using the OST function set it to switch every 6 hours on/off and named it tide. Then on the return pumps I can alternate the flow to the right and left side of my tank to simulate high and low tide without turning them on or off.
I think if you have the Apex and the flow fits, the Cor is a good pump. I also don't think you can go wrong witht eh new Vectra's.
