I used to have UV ones, and then green ones in different cases, and they look pretty damn good if done properly and you have the case for it
However, the only issue I'd have with using them today is they come with a lot of mess. An inverter and extra cables, plus a molex/4pin needed to power them. With how good I've got my 650D looking in terms of hiding cables now, I wouldn't want to ruin that despite being tempted just for a nice glow. To compromise I settled for Betfenix Red LED fans, not as bright but does a similar job