I'm still on stock firmware and have never used custom firmwares on routers before. Recently i found that i need to connect to my vpn directly through my router which isn't supported on stock firmware for rt-n56u. I know very little about what new functionalities I'd get from a custom firmware so i thought I'd ask here before flashing anything.
And if OpenWrt wouldn't give me a vpn client on the router, maybe some other custom firmware will that you could recommend.
Also, the stock firmware is from 2017, so is there any other benefit to using a newer custom firmware instead?
VPN support in general does not depend on the specific hardware (aside from providing enough flash/ RAM and CPU performance to match your throughput requirements), but is a generic software feature.
Yes, OpenWrt will run on your device (the rt2x00 WLAN drivers are a bit of a weak spot, but usable) and it will support various VPN protocols as needed. Depending on your WAN speed, it may perform below your expectations though, as a single core ramips (RT3662F) SOC running at 500 MHz isn't particularly fast for VPN uses (avoid OpenVPN and prefer IPsec or wireguard, if you can, as the later have significantly lower CPU requirements).
I think it currently allows for 300mbps on both bands concurrently and i got 100mbps dl, do you think it'll effect me a lot?
Since it has a weak spot using openwrt, do you know if any other custom firmware would be a better fit. I barely even know what's available out there
You will not get anywhere near 100 MBit/s while running a VPN client on your router, see Comparative Throughput Testing Including NAT, SQM, WireGuard, and OpenVPN for a rough idea (ath79 should be roughly comparable, if you account for its ~50% higher clockspeed and multiply the benchmark results by ~0.65 (no, you can't compare it quite that easily, but it will give you a ballpark figure - at least for VPN performance)).
VPN throughput maps pretty closely to the pure hardware performance, as neither ramips/rt3883 nor ath79 have any hardware acceleration for it. This also shouldn't differ that much between different firmwares (OEM (assuming it had VPN support) and OpenWrt or other alternatives). So your router's hardware performance will be the bottleneck for this purpose.
Do read https://openwrt.org/toh/asus/rt-n56u before flashing anything, as not all hardware revisions of this particular device seem to be supported.
That's disappointing to hear. If i buy a new router that has a vpn client, i should be able to use my whole 100mbps right?
Would you recommend getting any specific router?