Yep, if you are carrying 15+ discs in an Innova Competition Bag or equivalent, then backpack straps (backsavers/quads) are worth it IMO. My shoulder was giving me fits after playing, especially if playing 36holes or more. As soon as I got the backpack straps, no more shoulder pain. I recommend them.
I use the Innova BackSavers, and have been very pleased with the feel and durability, and they are about $15 less, so if you want this style of strap, and don't want to spend $40, the backsavers are a good alternative.
how long ago did you buy them?