comparison of most foods:
http://www.therabbithouse.com/diet/rabbit-food-comparison.asp
the best on the market is SS, but I worry about a choking risk due to how large the pellet is. excel is considered the second best. I think its something about the way that they're made but I can't recall why.
I personally wouldn't advise to feed muesli as selective feeding in any animal is dangerous as they're not having a balanced diet. I would suggest a pellet diet for all animals, even tiny hammies, although for the tiny robos they can be hard to find a good pellet for as most pellet is about as big as their paws!
every bunny is different, some bunnys even get a poopy butt on burgess, some on excel. every bunny is different.
generally its recommend 1 table spoon per KG of body weight a day, too much is bad but none at all wouldnt be good either.
RE the burgess indoor rabbit food, its "okay" but a bit of a marketing ploy. the issue is is that theres very little evidence that indoor rabbits have a vit D deficiency, most articles you find are from companies trying to sell their products. the most concerning thing however is that the product
has way too many vitamins in them. I think vitamin D had double if not triple the amount of vitamin D a adult rabbit should have. fed long term and it could cause more health issues than not, so I would personally advise others to steer away from it.