I have painted a buggy from the Tyranid Cultist line in 40k. I wanted to use it a militia kind of force but mostly I i got it just for the painting of it.
Its a neat model that I really like.
I didnt like the twin heavy stubber that was mounted on the hull so I exchanged it for a pintle mounted variant built from the base of a twin bolter and the barrels from the original heavy stubbers. I like this look far more.
I painted it to fit into a sort of red "marsian" type of dessert theme, with its camouflage and the red road dust.
In 40k I could use it in a force of desert militias using the Tyranid Cultis rules but skipping all the tyranid bits. Its just a smaller side projects so it doesnt need to be tournament competitive good.
In 30k I wants to build a smaller militia list, I havnt found any good rules for it yet. Its to big or rather to well armoured and looks to fast to represent a sentinel. Its to small for a Rhino equivalent type of vehicle and the 8wheeler in the fast attack slot feels also wrong.
But its a fun model and I like the end result.