I had a Hump (fnaaar !!), but it wasn't great. the press-studs tore away from the edging within about 3 months, and it let an alarming amount of water through. In the end I ruined it by putting it in the washing machine - and the lining came off like snow when I pulled it out.
Last Christmas I got a Creative Reflectives waterproof cover, and it's fantastic. Fits the sizes of rucksack that it claims to fit (unlike the Hump), and hasn't let in a drop.
Mind you, since May I've been using my much smaller and lighter Deuter Race EXP Air which has a built-in cover which has been totally resistant to the best the British summer threw at it. It's not reflective other than the Deuter logo on it, but I guess a few strips of reflective tape would suffice if I felt that my reflective waistcoat and very bright lights weren't enough.