This ICE is a nice alternative to Eli 1.0. Whilst Eli is a pain to get through (costing either 4 credits on corroder or two clicks), there are no consequences to messing up, beyond ending the run. You simply bounce.
Markus, by contrast, carries a powerful ability mitigated by the bioroid ability and the fact that the runner can choose. It is more of a taxing ICE than a stopping ICE, as the runner really won't want the ability to fire. Better comparisons would be Ichi 1.0 and Viktor 1.0: if the abilities fire, fantastic, but they are mostly there to force the runner to spend clicks and credits to avoid damaging effects.
Perhaps it should cost 3, but it does have some subtle advantages: it is the only barrier with a destroy effect (except Galahad with Lancelot), and it is also a card capable of destroying without actually being a destroyer (Only Taurus and Flare can claim the same). This allows it to get around sharpshooter. Finally, it can potentially destroy any card.
I would certainly consider running these in RP instead of Eli.