  Precise measurements of stellar parameters are required in order to develop
our theoretical understanding of stellar structure. These measurements enable
errors and uncertainties to be quantified in theoretical models and constrain
the physical interpretation of observed phenomena, such as the inflated radii
of low-mass stars.
  We use newly-available TESS light curves combined with published radial
velocity measurements to improve the characterization of 12 low mass eclipsing
binaries composed of an M~dwarf accompanied by a brighter F/G star. We present
and analyse ground-based simultaneous four-colour photometry for two targets.
Our results include the first measurements of the fundamental properties of two
of the systems. Light curve and radial velocity information were converted into
the physical parameters of each component of the systems using an isochrone
fitting method. We also derive the effective temperatures of the M~dwarfs,
almost tripling the number of such measurements.
  The results are discussed in the context of radius inflation. We find that
exquisite precision in the age estimation of young objects is required to
determine their inflation status. However, all but three of the objects are
securely located among the main sequence, demonstrating radius inflation and
the necessity to develop our understanding of the complex physical processes
governing the evolution of low-mass stars. We investigated the hypothesis that
luminosity is unaffected by the inflation problem but the findings were not
conclusive.
