Ill be using it at home. (hence the not caring about open/closed)
Well, the open cans have the driver placed outside and will act like a pair of mini speakers, so the sound leakage will definitely attract other members in the house if you're listening in the living room, for instance. However, the opposite is also true. When the surrounding is noisy, the clarity of whatever you're listening to will be affected (not really apparent, but noticeable nonetheless).
mobo/pc and some laptops[...]I may get an amp or a DAC in the future
I don't know how much benefit the headphones mentioned here will get (except the HD598), especially when your sources aren't really that weak (except maybe your phone?) but good luck, anyway. IMO, it'll be better in the long run to combine that money to reach the next range: AD900x is only around £160 (at UK or JP Amazon, not US) and will do just fine without an amp.
music/gaming and not monitoring or isolation[...]but a detachable cord is quite useful since i need a quite long cable and need to switch from my pc, to my laptop or phone.
Only if you don't mind with the small soundstage (compared to K550, being the same closed-backs).