You mean the reed itself is bronze? Are they old? I didn't think anyone made them anymore, but maybe they do. The very old accordions had some sort of brass/bronze reed. I've heard (no personal experience) than they are not very loud and don't hold a tune well, and break easily, which is why everyone I know of today makes steel reeds.
Could be, but hadn't heard of them in Hohner. Even being a lot thinner bases, they are noticeably heavier for even a half set like I put in mine. Lot's of different opinions on this, and probably depends a lot on the accordion itself, but some say they are louder, some say not, the ones I've installed seem clearer toned and quicker to respond, but others say little difference. They are usually quite a bit more expensive.
I actually saw an old hohner from the 20's, or perhaps even earlier, a few days ago with the "Steel Brass Reeds" stamped on the inside face plate. If that's what you're talking about I would stay far away. The reeds inside were all on four long plates as opposed to individual reeds and the reeds themselves did not put out much volume at all and looked very fragile compared to the old blue steel or modern reeds.
I've got 2 in my shop like that right now, they're novelties. What's odd abou those old reeds on the single plates, is the base side has as good a volume as todays reeds, but the treble is very weak. I wouldn't buy any reeds like that to put in a good accordion. Might be worth fixing up an old accordion because they have a neat old sound, but don't expect much performance.