While WTF explains a lot there's plenty left to be explained.
When you go into your inventory and upgrade your shields, targetting and other basic stats that will stay with the current armour you have equipped. It may be obvious once you have multiple armour suits but I thought the upgrades could transfer over. So it's best to wait til you can get a decent armour suit to begin upgrading, don't waste hundreds of credits on upgrading basic armour. Also it appears that armour paint jobs are only for custom armour and can not be applied to basic although the Canadian set will work on basic and does not appear to work on custom armour. I am going to look into this further I would like to use my Canadian paint job on my Sniper suit which is very cool by the way.
The second weapon the grappling hook is awesome for escaping when your cornered and for flanking or sneaking up on opponents. The third weapon is like a shot gun and great if you like to get up close and personal.
I like that the game itself is free and can be played completely free from start to finish, you only need to buy power packs if you want to level up or upgrade your equiptment faster. The game only makes money when a player enjoys it so much they are willing to buy more power packs and I think it will be a great money maker and show many other iPhone developers how to provide quality without compromising profit.
Feel free to add info to this guide and share your thoughts.