I once flashed the GX290 image and ended in a boot loop on my GX290+. The Mediatek tool chain and a initial image I could find in the wild.
I own a GX290 plus now for a while and it is the only real outdoor phone I have seen so far. Not to compare with any Samsung or equivalent. IP86 is one thing, MIL STD 810 G is just another level. Alloy frame, power bank functionality, wireless charging - all there. I use it on my offroad motorcycle for all kind of purposes under ALL conditions.
If I just could get rid of the preinstalled OS and use the beloved e.foundation just like on my FP3+
If e.foundation would make an official image, I would support this by purchasing another e Backer worth 128€. 
BR
Uwe