I like the signing, but this is absolutely a high-risk/high reward signing, regardless of the contract. The risk isn't financial; that signing him cripples the Twins financially if he comes up lame (like he has the last FIVE consecutive years, by the way.) The risk is that there currently isn't a backup plan for him.
So there is at least a 50/50 chance that this signing means nothing, which Twins fans would obviously (and justifiably) be irate about. ON the other hand, there is a chance that Zumaya is a dominant late-inning reliever. I like the signing - but I would like it a LOT more if another arm was added to mitigate the risk.