Instruction: Extract information from the supporting document to answer the given question.

Input:
Question: I want to use this strap while also carrying a backpack. Does this work okay or does having both straps over your shoulder cause comfort problems?
Document: The much heavier backpack I was carrying didn't have the same effect. Speaking of which, because of the way its designed, it doesn't work well with backpacks. If you put the backpack on first, you can't take off the backpack without setting down your camera on the ground first, or if you put the strap on first, you can't take it off without removing your backpack first. I've never had this problem with traditional neck straps.Another annoyance was that the length adjustment didn't hold very well.
Too skinny on the shoulder, makes the camera feel heavy. Got the regular full-sized RS as a replacement which makes the camera fit a lot better. Strap is also perhaps an inch too short for me (I'm 6'4&#34; though so it might work for you if you are shorter).
This strap is great. I use a canon 60D with the 18-200 lens. Its exactly what I expected and very comfortable to wear all day. I am really happy with this product. The pad is not too thick and the underarm strap can be removed easily. It is easy to adjust, and stays in place well. You can reverse it to the other shoulder, but it doesn't work as well. Definitely designed to hang on the left shoulder and have the camera at your right hip.
I bought this strap to replace my 4 or 5 year old original R strap which I lost :-(This strap is definitely an upgrade. The curved pad fits much nicer, and the under arm additional strap really stabilizes the strap if you need it. You can also easily take that strap off and use it loose, like the RS-4. The new ConnectR-2 is also an upgrade from my original.Many people complain about the price of BlackRapid straps but to me they are worth it.
I just got my Black Rapid today. How have I not found this thing before??? Pure genius!! I have walked all over numerous places in Europe, Alaska, and Central America with a standard neck strap tied around my wrist. And thinking I was doing well! LOL!And I put it on along with my mid-sized backpackers backpack as well and they will work just fine together, so I'm all set for the Inca Trail in a few weeks.
It's the only thing on the front side of the strap so I can easily without looking or thinking about it locate the clasp, open it, slide it down and re-clasp to lock my camera down.- Can be worn under my backpack no problem. This was a must.- Durable nylon straps.- Heavy duty plastic buckles.- The piece that connects to the camera is heavy duty metal. This sucker isn't going break.- Screw connector for camera is heavy duty.
I purchased a strap that can fit a man that allows a camera to hang at hip length....I'm 5'2...that's a lot of extra strap. There are clips to hold the bundled strap but weren't snug enough and they kept coming out and I had to stop and redo. This was bothersome. I don't want to cut the straps so I'll probably rig it with something to keep them in place.I am not going to say I came out of the hiking trip sore-free.
I ordered this prior to a vacation to China. I obviously wanted my DSLR with me the whole time, but did not want it  around my neck the whole time. I've tried putting the standard Canon neck strap across my chest but it was still difficult to quickly raise my camera and shoot. The RS Sport-2 is the perfect solution! It rests so comfortably on my shoulder at times I forgot it was even there. I can easily slide the camera from my hip to my face for quick shooting.
If you're reading through reviews of this product you're either deciding if you want to upgrade your camera strap (stock)for a sling-type or you've already made that decision and are trying to figure out which BlackRapid to buy. If you're still thinking on buying a BlackRapid stop... just buy one and feel the difference. There are tons of reviews already that talk about the enormous difference compared to the regular straps.
I needed a sling strap for my camera to use on hiking trips. I don't use the neck strap at all and prefer to use a small camera bag that fits just my camera that I can grab anytime I need to take a shot with a backpack or bag of gear in tow. For me this method is perfect for me.
Answer: I wear often with my fstopgear backpacks. I have no problems using my blackrapid strap. I typically where it under my backpack. On some occasions you may need to adjust, meaning a quick slide, not a big deal,  to make sure the retention underarm buckle isn't uncomfortable while wearing it under a pack. My blackrapids and fstop bags are like AMEX, I don't leave home without them.