  We prove a dichotomy for o-minimal fields $\mathcal{R}$, expanded by a
$T$-convex valuation ring (where $T$ is the theory of $\mathcal{R}$) and a
compatible monomial group. We show that if $T$ is power bounded, then this
expansion of $\mathcal{R}$ is model complete (assuming that $T$ is), it has a
distal theory, and the definable sets are geometrically tame. On the other
hand, if $\mathcal{R}$ defines an exponential function, then the natural
numbers are externally definable in our expansion, precluding any sort of model
theoretic tameness.
