The list of _satellite methods that is safe for DTM is here: Dynamic Tag Management Object Reference. The methods on that list are also safe to use in Launch - although .notify() and the three cookie-related messages have been deprecated in favor of the new .logger() function and a new cookie() function.
_satellite.browserinfo() is not on the list and will not be available within Launch.
A little of both. I put the browser, os and device type info into my data layer. I use that to decorate some of our API performance logging. I also use it in a couple of DTM rules. It is a handy way to get some basic info without having to parse the userAgent string myself. It won't be killer if it is not available in Launch, but it sure is convenient.
And speaking of the new cookie() function - where is the documentation on that? I looked, but no luck.
As a follow-up question, can I ask where exactly you're using it? Are you putting into custom code windows in DTM? Or using it directly within your applications/sites? I'm talking with the devs to see if there are other ways to get that information.