Claude, I think it maybe about the core technology being used. The NVT CLEER, EC10 and EC Link have been designed to support high MP and HD cameras. The trade off is distance.
Depending on the coax cable type, the NVT CLEER, EC10 and EC Link can deliver Fast Ethernet (100mbps symmetrical, full duplex) and PoE+ with distances of over 2,000 ft.
The trade off is distance. The new NVT IP product can provide robust bandwidth but the distance capabilities maybe shorter than other extender products. So it depends on the reach requirements that you have and the cable type.
If the project you are working on is within NVT product specs NVT would be glad to send you a pair to test and determine if it can help you with this requirements and report back your findings.
EC Link and EC 4 Data sheet
EC 10 - 10 Port Unmanaged switch
CLEER 24 - 24 Port Layer 2/3 EoC Managed Switch
Hope you find a resolution to your problem and that NVT can help.