Oh my bunnies are VERY picky about their salads. ^_^ And whenever I introduce something new, it always gets a judgmental sniff or the bunny butt. I think it’s just their way. Of course if it sits for too long and begins to wilt, I usually take it out and toss it (ahaha…tossed salad..lol) just so they don’t get ill if they do sample it.
Mimzy loves endive, but the other two won’t touch it. Fiver eats NO lettuce whatsoever anymore due to his cecal dysbiosis. Pip will eat anything, so I have to be very careful of what she does consume. She can get a good round of poopy butt from the most innocuous of vegetables.
Raddichio is an odd type of lettuce, more like a cabbage leaf. I don’t think any of my buns will eat that. No mater what stage of growth it is in. Maybe the spring mix is a set of younger leaves? If the other salad you were given contained the matured plants they may not have the same appeal.

Monkey usually snubs new foods, but with persistence, aka me shoving it at her face til she gets annoyed and grabs it to toss it thus finally tasting it, she learns to like more foods