I just did a 1-star LGTF over the weekend on Indomitable (shout out Indom Badge Runs at the link below) and we ran the first mission at +4/8 with a pick up team of 7 and no AT/powerset requirements. It was the first time for the majority of the players and my first time leading it (I've only ever soloed 1-star). Everyone seemed to do fine at that difficulty, but I went ahead and ran it at -1/1 for the rest of the TF because it was a badge(s) run. Surprisingly, the enemies actually changed to lower level and went to 7 player spawn size.
If any players are worried about difficulty, hopefully my anecdote gives them confidence to run advanced mode content. It's a lot of fun and there's really cool enemy encounters to enjoy.