no problem at all, it shoudnt give any problem... its an adapter so you can use it without any problem... feel free tod o it... but i would never use a device connected to any usb port as a boot device...
i would recomend to use pcie to sata adapters instead if you have any pcie x1 free slot... sometimes is safer to have it inside than outside...
also if you have any 3.5/5.25 bay not in use, there are many usb 3.0... bays/adapters... etc... some brands even have a dual 3.5hdd + 2.5 hdd to be pluged in a single 5.25 bay with 2 usb 3.0 for around 40$...
there are some pcie x1 to usb 3.0 and mobo expantion options, depending your case...
examples:
http://www.amazon.com/Anker%C2%AE-Front-Panel-Connector-Adapter/dp/B00J4EZE4U/ref=sr_1_2?ie=UTF8&qid=1428191087&sr=8-2&keywords=3.5+usb+3.0
http://www.amazon.com/Syba-5-25-Inch-3-5-Inch-2-5-Inch-SY-MRA55006/dp/B00834SJ8K/ref=sr_1_2?ie=UTF8&qid=1428190908&sr=8-2&keywords=5.25+usb+3.0
http://www.amazon.com/Crest-Port-SATA-PCI-Express-SY-PEX40039/dp/B005B0A6ZS/ref=sr_1_3?ie=UTF8&qid=1428191139&sr=8-3&keywords=pcie+x1+sata
http://www.amazon.com/Anker%C2%AE-Uspeed-Express-20-pin-Connector/dp/B007SJGGAE/ref=sr_1_2?ie=UTF8&qid=1428191327&sr=8-2&keywords=pcie+x1+usb+3.0