Many of the gl.inet routers can run vanilla OpenWRT out of the box—the linked router above (Beryl) included[1]. Be mindful that not every one of their routers can as some run unsupported chipsets that require a custom build, but many do. Can always check for support on the OpenWRT page for gl.inet routers[2].
Just here to second the recommendation. I'm in no way affiliated, I've just happily used several generations of their routers for this exact purpose.
EDIT: Wanted to point out that their newest and most powerful travel router with (upcoming—in the latest v23 release candidate[3]) support from mainline OpenWRT is the Beryl AX (GL-MT3000)[4].