units is often "branded" by ISPs. This can lead to several performance bottlenecks that a generic or updated firmware version solves:
binwalk -e firmware.bin # or if encrypted, you may need to decrypt first
The stock software often chooses a congested frequency band. Manual band locking can drastically increase speeds.
Using unofficial firmware can "brick" your device or expose it to security risks. TeamViewer What "Better" Firmware Typically Improves Network Band Locking