Are the quick release buckles safe?

Yes, they are made with a strong Acetal plastic that locks together. You have to squeeze both sides together at the same time to release the buckle so there is no chance of it accidentally releasing. They nylon webbing is tested at 600 lbs. and the whole strap has been tested at 75 pounds. More tests are in process. The quick release straps attach to your camera the same way your current slr and dslr straps attach, there is just a buckle halfway up the 2 1/2 inch nylon portion. If you would rather, you can choose to purchase a strap without the quick release nylon webbing. Just note that in your purchase.

What length should I get?

The straps I offer(32 & 38 inch) are usually longer than your stock camera strap(approx. 30 inches). They are created longer so they can be worn across your body instead of around your neck. This is great for those who suffer from neck and back pain. Wearing the camera across your body takes the stress off your neck and back and shoulders. If you need a different length, just let me know, I'm glad to work with you.