That doesn't sound like ADSL(2+). I'm pretty sure that we are talking about VDSL (maybe even with Vectoring).
Please make sure which type of connection we are talking about...
Afaik this device isn't supported by OpenWRT yet... So if you want something which is compatible with OpenWRT you will have to buy a different device.
For a cheap device maybe take a look at the following Thread: https://forum.openwrt.org/t/whats-your-favourite-cheap-lede-openwrt-device/
But as a OpenWRT beginner I would recommend you something like a WRT3200ACM or Netgear R7800 which have both great OpenWRT support and stable + frequently updated community builds.
A used/refurbished Linksys WRT1900AC/ACS would also be a option (but I'm not sure if you will find an offer within your budget) or a TP-Link Archer C2600.
For recommendations take a look at the following thread: EU VPN Provider with Wireguard support?