The problem with juries is that they are also quite biased, and tend to flock to a certain opinion about the crime depending on the appearance of the suspect. You are looking black and charged for murder? Congratulations, the chances you will get the death penalty are much higher than with white people:
The majority of prisoners in American jails are hispanic or black, white they are a minority in the population. Is this all explainable only by less economical chances, which tends to a higher crime rate, or isn't there something else also going on? Does the majority of the population really commit less crimes than the minority?
Juries are black boxes. You'll never know why they think that you are guilty, you only know that you do. In case you do appeal this means that arguing against the verdict is hard, while a professional judge will give you a detailed explanation for the reasons why.
Juries are expensive; and so they do make even simple trials expensive.
Juries can be manipulated.
And of course first you need to be able to find enough jurors.
This is why I don't think that juries deciding on guilty or not guilty are a good idea; I do prefer professional judges over them any time, maybe with an advisory jury at place, if needed.
And I do prefer the Austrian way on how to deal with a jury: it's only part of the legal process, if the offense is heavy enough. Then you've got three professional judges and eight jurors. The jury only decides with simple majority guilty or not, and together with the judges on the penalty together.
If its 4:4, the culprit is being considered innocent. If the three judges all think that the decision of the jury is flawed, then they can veto it, which gives the jurors the opportunity to decide on it again. If this doesn't resolve the caveats of the judges, it is being relayed to another court.