I've been commuting LON - EDI for 2 years now, frequently doing 2 returns a week.

It's not to be taken lightly - indeed I wouldn't recommend it for longer than a year. Having lounge access undoubtedly helps but only a little as you'll refine your travel routine to spend as little time at the airport as possible. (I tend to use LCY anyway). As others have said, some flexibility on your employer's part will be important (I tend to stick to 2 nights away at most and find this to be just about bearable).

It is also much easier in summer than winter.

Good luck!