I can't tell you how much I liked doing Math Workshop this way this past school year. Not every single day, but many days - and the kids always seemed to prefer the days we did Math Workshop rotations!
I alternated between mixed groups and leveled groups and did a three-way rotation. With leveled groups, the low group was the "Grupo Azul." They started by playing the math game with someone else to warm up and practice. The high group was the "Grupo Amarillo" since they were usually capable of completing the math work alone without too much teacher guidance. Other times I would have them in mixed groupings so the higher kids could coach the lower kids.
Either way, it was SOOOO nice to only focus on 1/3 of the class at a time and really ensure they understood the concept for the day! I could also differentiate better for their levels. Lots of flexibility for me. All you need is a small pocket chart (the kinds they have at the Dollar Tree), a whiteboard where you write the day's tasks, and the kids divided into the three colored groups.
Hope this is useful to you or gives you some ideas for your own math workshop!