How useful is this skill? Is it worth to get any points in it at all?
PS: Next time use the search 
From personal experience the way it works is if you have a lv1 Key but lv5 Unlock Chest that lv1 key can open chests lv1~5. you need a key to use it so if there isn’t a way to get more keys then this skill becomes useless at some point.
You can sort of farm the chests since there are some that continue to respawn. the respawn time I don’t know but I did open the same chest more then once just coming back everyday trying to see what I woud get.
I’ve gotten 3 different items (not at the sametime) multiple times from a lv4 chest so I’m going to assume there is a set loot table for every chest and each item in these chest have different percentages of being obtained.
This is from my experience during icbt2 lv200 Corsair C2 the way the skill works might have changed I’m not sure since I haven’t been keeping track of any KOBT info.
with the increase in lvl limit im sure there are lvl 6 chests to farm. just saying it is a different way of making money off of your class, as long as not that many people are going for it
Very interesting. How good was the loot you achieved from the chests?
well in icbt2 the collecture sword, flamburge, and there one some spontoon recipe, sold for a good deal of money
This skill useless for now because high lvl key is available, either from quest/boss fight. Mybe in future it will be useful or high lvl key need some hidden trick to get it.
the only thing good is atttibute +3 speed walk for 7 seconds. lv1 is more than enough. the attribute might useful in pvp.
why my corsair can’t do fast attack (C1).