geek talk follows ;-)
guys, myself i have claro adsl and ftth as well as delancer and all those modems do their work just fine as long as you understand that it is made to get you connected and authenticated in the network not much more than that. i have to reboot even cisco ones at times. any heavy use requires dedicated router with enough resources to support it. for example if you use P2P, and a bit less damaging VoIP apps one single app creates or attempts to create so many connections that it can overload the modem with ease. it is recommended to reboot modem after p2p use so it can start with clean table. also with wifi because the way this technology works devices with bad signal can ruin experience for everybody connected to your wifi.
big ISPs require customers who wants stability of their network to purchase expensive (relatively) routers it's because even those more expensive ones can take only that much of load. and load is not necessary to be speed - it could be just amount of connections per second and multiple wifi chains running together or just ability to withstand attacks that constantly happening when you get online.
because of shortage of IPv4 address space the only public ip address gets your modem and not your computer, so all connections that any of your devices make require your modem to remember so it can be translated. That's why IPv6 was introduced and i don't know if you noticed pretty much every customer of delancer who has dominican ip addres gets IPv6 not just address but set of networks which means that every single device that supports it get true public ip address - which means modem doesn't need to remember anything other than your mapping of your mac and ip address and it means Point-to-Point connections can be made directly without address translation magic and means less use of modem's resources.
that ZTE that
@chico bill is not happy about with correctly setup local network can handle 700Mbps. here is example of lab test i have done: i intentionally used another ISP's server:
upload