  We present a comprehensive Small Angle Neutron Scattering (SANS) and Neutron
Spin Echo Spectroscopy (NSE) study of the structural and dynamical aspects of
the helimagnetic transition in Fe$_{1-x}$Co$_x$Si with $x$ = 0.30. In contrast
to the sharp transition observed in the archetype chiral magnet MnSi, the
transition in Fe$_{1-x}$Co$_x$Si is gradual and long-range helimagnetic
ordering coexists with short-range correlations over a wide temperature range.
The dynamics are more complex than in MnSi and involve long relaxation times
with a stretched exponential relaxation which persists even under magnetic
field. These results in conjunction with an analysis of the hierarchy of the
relevant length scales show that the helimagnetic transition in
Fe$_{1-x}$Co$_x$Si differs substantially from the transition in MnSi and
question the validity of a universal approach to the helimagnetic transition in
chiral magnets.
