Hello,
It is really unusual that device bricks when installing the latest firmware correctly. Even if you will get very unfortunate and somehow brick your device it is possible to recover and fix your device so do not worry about that.
Regarding your question about PoE support, TRB140 from batch 12 and all the following batches have PoE support. Most likely when you buy the device you will get a device from the newer batch.
Regards.