They work fine as a regular HDD
difference between normal and RED (nas) drives is Price and some Hardware level error correction stuff for raid solution
RED drives also run at 5400 RPM, have 3 year warranty and lower MTBF ratings from the enterprise drives (7200 RPM, 5 year warranty and higher MTBFs). Enterprise discs are more expensive but aside from other features, the increased speed and better warranty should make-up for their increased cost and they also include the time-limited error recovery (TLER) feature which is included in the RED drives.
See this table to compare features: http://www.anandtech.com/show/7258/battle-of-the-4-tb-nas-drives-wd-red-and-seagate-nas-hdd-faceoff/2