Public defenders do not hire their own experts, they file a motion for expenses and the court approves a $ amount and they use that to hire the expert. Its paid for by the county. If its a breath test case than the intoxilyzer expert is going to be called by the State anyway and that is an expert that both sides can use for everything from the science of the machine to the effects of alcohol on the body.
I would not say that any prosecutor or any PD or any retained attorney for that matter is necessarily well versed in DWI. Its true that DWI is tried more often than any other case but its also the most complicated kind of case to try. I've tried DWI cases that have lasted longer than murder cases. But generally speaking, a PD should at least be able to hold their own in a DWI or they should not be on the appointment list.
Here's the thing with public defenders, they are representing you for one of two reasons. Either its because they genuinely want to do public service or because they want to get their name out there in the "world of defendants," because if you like their service than you will tell your friends and that will bring him business. Either way the incentive to do well in your case is there.
