It seems ironic that the little stars are so feisty, but less ironic if you ever had a Chihuahua. [not me!]
From what I can gather, red dwarfs have fully convective atmospheres, unlike larger stars like the Sun. The red dwarf's rapid spin generates large mag. fields that suppress the downward, cooling action of the convective flows. As mag. fields entangle -- I assume differential rotation exists on red dwarfs, too -- then they can generate huge potential fields that eventually snap.
Once it was learned that the blasts were mostly intense in the higher energy bands (UV and above) then more attention was given to red dwarf flares. Earlier observations showed very little changes in the visible band so it was assumed they weren't that feisty. It seems, however, that they are very common, including monster flares.
An orbiting planet in the HZ will suffer greatly even though they are likely tidally locked. Atmospheres could be blown away in time. Abiogenesis would seem highly unlikely given the destructive power of UV and higher energy photons.