  We explore the observational adequacy of a class of Unified Dark
Energy/Matter (UDE/M) models with a fast transition. Our constraints are set
using a combination of geometric probes, some low redshift ones, and some high
redshift ones (CMB related included). The transition is phenomenologically
modeled by two different transition functions corresponding to a fast and to an
ultra-fast transition respectively. We find that the key parameters governing
the transition can be well constrained, and from the statistical point of view
it follows that the models cannot be discarded when compared to $\Lambda$CDM.
We find the intriguing result that standard/input parameters such as $\Omega_m$
and $\Omega_b$ are far better constrained than in $\Lambda$CDM, and this is the
case for the derived/output parameter measuring the deceleration value at
present, $q_0$.
