Without a comparison to a commercial developer, it's very hard to tell what the effect on the negatives are. The roll of 120 he held up looked very dense to me, and looked like it was suffering from a fair degree of fogging between the frames. Saying that, if he's scanning the negatives there's plenty you can do in post to pull an image off of the negative.
I'll stick with Xtol as my developer of choice, but that's just because i've been using it for such a long time it's a habit rather than an informed choice from having compared the options today :) Funnily enough it's active ingredient is ascorbic acid as far as i'm aware (vitamin C).
Caffenol is a pretty popular technique, you can find many detailed posts online comparing it with other developers.
I've used it a few times in a pinch when traveling, it's nice. Unfortunately I've never been able to find a fixer formula that's as easy/off the shelf.
I'll stick with Xtol as my developer of choice, but that's just because i've been using it for such a long time it's a habit rather than an informed choice from having compared the options today :) Funnily enough it's active ingredient is ascorbic acid as far as i'm aware (vitamin C).