Setup:* 27" iMac 5k with TB2 ports.* HighPoint RocketStor 6661A* Third party PCIe to NVME adapter* Generic 1TB NVME & SSD in a USB 3.0 case (for APFS Fusion)Some Pros: Quiet or the fans don't work. Solid build. Easy to get into the device. Discreet. No crazy vibrations. (I don't like fan or drive vibrations)Cons: No On/Off switch. These devices (external chassis) still have a low adoption and the information out there only focuses on graphics. The one that did focus on NVME did not cover this information.Now for the TL;DR user experience:I wanted to future proof myself with a Thunderbolt 3 expansion to use with my 27" iMac 5k (late 2015). I was very nervous at first since the device had poor reviews. I've had it for 2 weeks now and it's had there has been a fair share of issues but I wouldn't say all of them are Highpoint's fault.I used the Apple TB3 (USB-C) to TB2 adapter to get this to work on my iMac with TB2. I placed a Vantec PCIe card in the enclosure and used a generic 256GB Inland Professional NVME I took out of my Windows box. At this point, I had a secondary SSD in a TB2 dock form a different Vendor. My first step was to even see if macOS saw the device. When I first turned it on, it did not recognize or power up. I was starting to get nervous. For some reason it did not like the Apple TB2 cable. I swapped it out with a 3rd party TB2 cable that I previously purchased. Voila. There's the device.I reformatted macOS and set it up to use the combined 480GB OCZ SSD w/ 256Gb Inland NVME. This setup worked like a charm but it had issues returning from sleep. This is apparently a known issue on a lot of devices. It's not just Highpoint. I got around this by turning off certain power settings such as auto shutoff, standby, and hibernation modes using pmset. Now It was working brilliantly. However, the NVME was only 256GB and I wanted more...I decided to take the TB2 dock back and buy a 1TB NVME instead. The original OCZ 470GB SSD was using USB 3.0 and I wanted to try the TB2 dock. I couldn't afford both the dock and the enclosure though. Now to get macOS on a new APFS Fusion drive using the 1TB NVME plus the OCZ SSD (now in a USB 3.0 enclosure). That's when all the troubles started.The fusion was created automatically and set the 1TB to the "main" device and the 480GB to the "Secondary (Aux" device. (Personally I wish APFS could span drives or use JBOD similar to Windows Storage Spaces. Right now it defaults to Fusion.) Over the next few days, I would have to unplug the Highpoint, cross my fingers, and hope I could option boot and see the drive during selection. Otherwise I'd get the folder with the blinking question mark or have to reset PRAM.Being an old timer Mac guy, I remembered that Macs would scan ports in a specific order during boot time. This apparently never changed from the old SCSI days. I started wondering if the Thunderbolt is last on the chain. I checked disk utility and found the synthesized APFS fusion drive was showing up as USB. Below that was the container and volume. Each were showing up as PCIe. I knew that had to be an issue. Apparently, it was scanning the USB device first before getting to the TB3 device and that in turn led to the question mark. It couldn't find the system on the USB device because the system resided on the NVME. I reformatted and reinstalled but it always showed up the same.You are probably wondering why even set it up that way. Well even with TB2, NVME, and a USB SSD, I was getting ~1200MB/s write and ~1400MB/s read. Together they made up 1.5TB of solid state love. That's a lot of space. What can I say? I am a glutton for space (punishment).Unfortunately, I had to redo the whole installation and manually create the APFS fusion drive so that the slower 480GB SSD was the "main" device and the 1TB NVME was the secondary (Aux) device. Voila! Now it boots up fine. It still doesn't respond to sleep well. That's a known issue though. It's not just Highpoint and I *did* use a generic NVME. (Inland Premium without firmware patches)Is it fast? Not as fast as the original setup but that's only when benchmarking. It's fast when booting up. When starting apps, I get about one bounce. Sometimes no bounce. So yeah. That's fast. Plus maybe it's better to have the secondary drive this way to prevent overall wear on that drive.I will report back in about a month. Fingers crossed.