Those are fine when you are in a pinch. Sometimes when I am in a rush I will grab pre-bagged salad mixes. Just be careful on the veggies with high oxalic acid (Leafy Greens 1 on the HRS list http://www.rabbit.org/care/veggies.html). Typically Spring Mixes have a lot of spinach and you want to make sure to give that in small doses.
It’s actually MUCH cheaper to buy bunches of romaine, red lettuce, parsley, etc. I chop them up and keep them in a big tupperware container in my fridge so I can just grab a large handful in the morning for breakfast and again at dinner for my bun. It’s a lot cheaper (lettuce is about 99 cents right now in Cali and herbs are about 59 cents a bunch).
Hope that helps!
EDIT TO ADD: Also, I 2nd the ‘start slowly’ thing. Introduce new veggies slowly into the diet – if your rabbit hasn’t had them before it’s best to take it slow so they don’t get upset tummies. Also, I sometimes like to give my veggies a good wash with water before I give them to Lola before I feed them to her if she isn’t drinking what I think is enough water – it’s a sneaky way for her to get a lot of hydration while eating her favorite greens. The girl is a cilantro monster! 