Certain aspects of it. You don't know what you're talking about because you don't understand the stat yourself.
The issues with UZR are 1B because of sample size, and SS, in which case the formula needs tweaking because it overvalues park factors.
It's a reliable statistic when used with players withconsiderable sample sizes in all three OF positions, 3B and 2B. It's acceptable when used with 1B with a large sample, and hit-or-miss with SS. Take the time to read about it so you can come up with a reasonable and informed opinion on it instead of bashing it mindlessly without understanding it.
Can't handle balls you can't get to.