Is it a must to buy the pifi kit to use this or can I reasonably get by with just downloading this to my pi4?
Hi, no, it’s entirely optional.
Core features — WireGuard, OpenVPN, AdGuard Home, OpenWrt, and the app — all work with the free firmware. You can download it here and flash it via Pi imager.
Wireless pairing — if you want to connect to a wireless network (e.g. a hotel Wi-Fi) and broadcast your own network at the same time, that’s not possible without the PiFi Kit. There’s only one radio onboard.
While it’s technically possible to try third-party adapters with OpenWrt, in practice it’s tricky and usually performs poorly due to limited driver support.
Performance — the PiFi adapter also delivers a major speed boost (especially on the Pi 4, where the built-in Wi-Fi is quite weak), often up to 8× faster.
But I’d recommend downloading it and having a go, it’s pretty competant with or without the Kit.