I bought the Soundwear 48 Bass bag for my Weltmeister Rubin. Although that's a 60-bass accordion, it's the size of a 48-bass.
Unfortunately the bag is about 1cm too short to fit the Rubin and the top zip can't close, and so I'm having to return the bag.
That's a shame, as other than that the bag looks to be really good. The front two pockets have loads of individual small sections, many with their own zips, to hold anything you might need. And the larger pocket easily takes A4-sized music books.
The materials are strong, as are the zips, and the padding is really thick. I also appreciate there's a chest strap for easy carrying over longer distances.
I think the reflective strip is a good safety feature, something that seems to be missing from other bag designs.