There is an FAQ for the Linear switches that should be of help (this is a clickable link)
As far as other brands, there are several other zwave brands that make master/auxiliary pairs for three-way set ups. So you have quite a few choices, just depending on the exact features that you were looking for. See The following thread. The light switch discussion starts around post 40:
Note, however, that you should always use the auxiliary which is designed to go with the specific master you were using. You can’t typically mix-and-match brands because they use different types of wiring.
If you don’t want to use the auxiliary position to control the master switch, you can use it for anything else as long as the device that you put there does have its own connection to the smartthings hub. The linear auxiliary is popular for this purpose as it cost a few dollars less than a master switch. But there are other brands that you can use as well. In these cases the auxiliary talks to the hub and then you set it up through the official smart lighting feature or some other smartapp to control anything else which can also talk to the smartthings hub. 
You do need to read the product descriptions carefully, however, because some brands, such as GE, do not put a radio in their auxiliary switches. Instead, the auxiliary communicates to its master through a physical traveler wire. Since the auxiliary doesn’t have a radio, it’s invisible to smartthings, and you can’t use it for any purpose other than controlling its related master switch.
But for auxiliaries like the one from Linear/go control which do have their own radio, you can use it as an independent device if you want.