I imagine it "fits" OK the question is whether it is classified or listed on the label in the box.
I think the BR breakers from Cutler Hammer are the ones you can use. I seem to remember they bought Bryant (hence the BR) but keeping track of who bought whom is as hard as remembering which bank used to be which.
Will it fit? Yes, but doubt it is UL classified for Bryant, use a Cutler-Hammer BR as they are the successor of Bryant/Westinghouse loadcenters. Because of mergers of electrical equipment manufacturers it can be hard to know which breaker fits what panel.
Norcal: You stole my thunder!! Comments heard over time by a few 'lectricians like 'Sir...it has to be OK, it fits on the buss'; 'GE breakers fit a lot of panels, so my boss said....'; 'Murry, Bryant, Challenger, T&B, Crouse Hinds, heck they all look the same'.
The classic used to be the guys who field modified the various rejection tabs, or butched the plastic to get the buss to fit,
Siemens/Murray are now what was Arrow Hart, Gould, ITE, Crouse Hinds, and IIRC, Sears "Homart" brand (I think was a relabeled Murray panel, someone correct me if I'm wrong) Cutler Hammer (or EATON as the newer breakers are now showing exclusively) took over Bryant, Westinghouse and one other brand I think..
I've always wondered why All the above manufacturers have designed their breakers to fit GE THQP panels with the t slot in the bottom. GE is the only company I've ever found where this would be needed
There are breakers made by 1 manufacturer that are also approved as a replacement for breakers in other manufacturer panels. Unfortuneately I don't have a defined list as it is fairly extensive in the 15 and 20 amp sizes.
There are the legacy breakers too so Eaton covers westinghouse, nova, and Bryant panels.
I thought that the breaker you are talking about is the Bryant BR type breakers. I think they were listed for many panels. The were the typical square black breaker that fits, Seimans, Bryant, GE, Square D home style.
They do say that they are UL listed at the bottom of page 4, but that seems to be a bit "buried", if you know what I mean. I'd think that they'd be boasting the word all over the place if this really was the case. They are going out of their way to be defensive, which to me is a case of 'thou dost protest too much'.