I cycle between towns and gigs with my accordion on my back. After trying many gigbags the Soundwear Performer has proven to be the one.
First of all the straps are solid, so they will always be there. You can feel the quality of the material. It will hold the weight.
It feels weather resistant. (I wouldn't say waterproof) but I cycled under light rain for hours and it was bone dry inside.
There is a soft padding on the inside to keep your instrument extra protected and the way it closes with the straps on top makes sure that it will stay properly closed.
There is also two front pockets that have a lot of room, and the very front is from a thicker harder material, so your delicate gear will be protected (I carry cables, flutes and harmonicas on this pockets)
The zippers are also solid, they are resistant and thicker, as my previous zippers from the lat bag were too soft.
Pros: All listed above
Cons: For all this protecting it would be slightly heavier than an ordinary bag, but safety first
Totally worth it.