Greetings @Nash and @DQ-Cisco ,
"Brand new" here means that the unit is new from the distribution center, or never unboxed, and never upgraded. The brand new units will come with an older firmware on it that has a risk of becoming inoperable if it is upgraded directly to the MX14-45 to MX14-50 RC firmwares. We recommended that networks upgrade the unit to MX14-40 GA first. Essentially, the recommended prerequisite for MX14-45 to MX14-50 RC versions is a MX14-40 GA base for these factory fresh units. We are working on a fix that will be sometime soon in the next MX14.5X version that will make this prerequisite not needed. If you follow this upgrade process, it is safe for these units to run MX14-50 RC.
As per any new firmware, please note any outstanding bugs that are still present in MX14-50 RC or whichever firmware you intend to upgrade to.