well… The T20 is the fully open back. T40 is fully closed and T50 is the semi open back and considered to sound the best, subjectively of course.
as long as your aware that it’s a very warm headphone and may be more towards dark instead of bright if your ok with that then ya it’s actually really nice…
Not sure, maybe someone here can clarify on that but I will say they are very difficult to drive. Though if you get the T40s at their base form you can contact Modhouse and have them converted into an Argon which are stupidly great. Dunno if you can have them keep them closed back though as I think the regular argons are semi open iirc you should be able to though so they keep their isolation. Dekoni Blues may be more up your alley though if you want a bright signature, you can mod them to be closed back since these headphones are known to just be heavily moddable.