As a rule of thumb, I don't install any "extra software" that comes with a free program. However, what you're seeing may not be malicious. It depends on what its telling you, and exactly what browser it wants to install.
If you can provide some more specific info, we'd be able to get you a better answer.
Going on what you've said so far, I'd recommend just getting a new bittorrent client. In the several years I've torrented, I've never had a program force an update or prompt a browser install during an update. If that is, indeed, whats going on, just dump the client. There are plenty out there that wouldn't make you upgrade or install frivolous software.