I fly with a EFVS (combined in a HUD) for work. It has its uses, but definitely has its limitations. The biggest drawback is that it does not do well with wet particulates (clouds). I don't think it would be very useful at all for detecting embedded thunderstorms because the cloud would wash out any forward vision you may have.
It will penetrate through the thinner bottoms of clouds and that's really why we have it. With the EFVS, we're allowed to start an approach with less than the minimum required on the the IAP, and we are also allowed to continue below the DA using only EFVS cues to 100' AFE, at which time we have to have natural vision to land.
Where the EFVS shines is in dry stuff like smoke, smog, haze. It cuts right through that and makes Bejing, Delhi, etc. look CAVU. Also good at night being able to look out and see towering CU and being able to deviate around them visually.