  Cosmological models with Lagrange multipliers are appealing because they
could explain the behaviour of the dark sector in a unified way. In this work
we analyse extensions to the "Dust of Dark Energy model" proposed in
arXiv:1003.5751 by including spatial curvature and more general potentials of
the scalar field. We perform dynamical system analysis and we determine the
evolution of the equation of state parameter as a function of the scale factor.
We present observational constraints on this model by using Union2.1 dataset
and H(z) data.
