@Sadlyshesaid It is generally only Classic customisations, which are customisations that you could also obtain in GW1, but the Keys will help you to do the Trials of Gnomus and unlock secret characters. Only the most expensive Rainbow Star chest will have a chance (but it is high) of giving you a Key when you open it. I suggest only opening the other one if you wish to play a Town Hall event enough, so that you get more use of your Rainbow Stars and do not keep them maxed out. However, I cannot confirm this myself, but you may also be able to get Super Rare customisations in the Town Hall chest packs.