The Flint v2's MediaTek SOC is supported by OWRT. MediaTek has a better reputation with F/OSS & Linux than most. The Flint v3 relies on Qualcomm's proprietary SDK for its performance. The Slate AX & Slate 7, both travel routers, also uses QSDK with GL stock firmware. It took roughly more than 2 years for OpenWrt devs to get it to a point a OWRT SNAPSHOT is now able to run on the Slate AX. The Beryl AX, another travel router but with a MediaTek SOC, had support long before that.
If/when you flash pure OWRT on a GL device it is critical you only use the sysupgrade tagged releases. Other versions put you at risk of bricking it.
I would say it depends on your urgency but if I needed something ASAP with onboard AP/Wi-Fi it'd be the Flint v2. I'm never going to waste time on QSDK-based devices again.
Regarding Stangri's PBR & pure OWRT performance you should read this thread... closely. It'll answer questions I'm sure you don't even know you have: