As for what they would do this is what I imagine.
Bismuth: When you burn this, the next metal burns at half it's original rate, allowing longer usage of it. However, once it begins burning, you cannot stop burning it until it's all gone.
Rosallum: Making the metals of your allies burn slower, though their metals will continue to burn until used up against their will.
Cobalt: Let's you show someone of your choice a future event taking place in the foreseeable future. It's not much that you are seeing shadows (like with Atium), more, they see images and vague impressions. This may or may not be useful since it may show either an unimportant event or something vital.
Stellite: Let's you show others events in their past. This may be useful in showing others past information that they have forgotten, or it can be simply for the other person to recollect.
Magnesium: Let's you send out impression of thought or speech into the minds of someone within your eyesight. This can allow for secretive communications as wells as making plans without being heard. Though it's uses are not as numerous unless someone else can also burn this metal.
Magnox: Opens your mind, allowing free thoughts to flow in. In other words, for those who are easily susceptible to emotional allomancy, their thoughts will not be as private as they may think if someone around is burning Magnox.
Nickel: Allows the one burning it to self purify their blood. This allows the curing or eradication of certain diseases and poisons. Also, it can burn away excess matter in the blood stream that may prove fatal. It cannot effect Hemalurgic Spikes. The metal burns remarkably fast, so full purification requires either a couple beads burned over a certain period of time or two Duralumin Bursts for fast action.
Iconel: Allows you to purify the blood of an ally though physical contact. By placing the hands on the chest or stomach, they may replicate effects similar to nickel. It burns just a tad bit slower than it's base metal counterpart, however, It takes a bit longer for the person being purified to be cured, though two Duralumin bursts aught to do it. However, Duralumin bursts leave the effected or yourself (with both metals) exhausted rather than burning it slowly and letting it steadily but surely burn out of your system.