If you're using Dahua cameras, the only sane NVR choice is a Dahua NVR, otherwise you lose access to some of the best camera features. I think most of us on the forum with Dahua NVRs are running aome variant of the 52xx series, and I have the sense the 5216 is the most common. Some run the 42xx series, which is a cost/performance/features tradeoff. I've used a version 1 5216-4ks2 for a few years. It has had crash/hang type failures less than once a year leading me to say it has stellar reliability. As with all of NVRs and cameras, the firmware is buggy. If there are bugs in a feature you care about it can be maddening, or you could be lucky and not run into the bugs. The other decisions are (1) How many ports, and (2) Built-in or external POE switch. If your friend already has 16 cameras planned it might be wise to get a 32 channel NVR. Otherwise he's stuck if ever wanting to add another camera. On the POE switch, I prefer using an external switch for 3 reasons: (1) Less money tied up in the NVR makes it less painful to change it out, (2) Don't have to replace the NVR is the switch fails, (3) Loud NVR fan if switch is built in. The system is more plug-and-play with the built-in POE switch, and there are probably other good arguments for it I'm not familiar with. Based on forum posts, the biggest issue with Dahua NVRs is when there a problem while trying to install a firmware upgrade.