As one reviewer put it after a few months of use: "a new one got a little hot. The breaks... are due to the provider and the line. I have been using it for 3 years and I love it". While many praised its reliability, the heat was a consistent observation.
The most reliable place is the D-Link FTP Site (specifically the /pub/ADSL/DSL-2520U/Firmware/ section).
The DSL-2520U is a classic ADSL2/2+ modem router, a device that was popular for its combination of essential features. It offered high-speed internet access for home and small offices, featuring NAT and SPI firewalls, Quality of Service (QoS) for traffic prioritization, VPN pass-through, and both Ethernet and USB interfaces. Many users chose it for its low cost and overall convenience.