- VDSL2 modem/router/firewall, an all-in-one box.
- VPN able.
- DDNS able.
- ISP independent.
- Broadcom chipset.
- Cost not to exceed £100.
I believe the TP-Link Archer VR600 v2 meets all these requirements. Indeed, my requirements were very similar hence why I bought one myself several years ago. A few things to note though:
The VR600 v2 has a built in OpenVPN server and PPTP VPN server, but the v1 does not. I got stung by this when I ordered one shortly after the v2 came out and ended up receiving a v1. I now use a raspberry pi as an OpenVPN server, so if you want to avoid this perhaps buy from somewhere with a good returns policy in case you get a v1 (unlikely though, the v2 has been out for a few years now).
While it does have a Broadcom chipset, the telnet cli is locked down so by default DSLstats and the like won't work. This certainly can be unlocked (instructions are on this forum) in the case of the VR600 v1 since this is what I have running now, so might be possible for the v2 too. I believe some members have successfully unlocked the telnet interface of the VR900 too. The VR900 also meets all your requirements, but is slightly more expensive for the benefit of faster Wi-Fi, but given that you have separate access points this is probably not a worthwhile upgrade.
I use my VR600 with the DuckDNS DDNS service, but there is a "NO-IP" option in the GUI too so this should work for you.