If you can get a better discount through CRO, you can weigh the chance that you may have to change rooms. I've done it both ways and didn't have to change rooms either way but it's a possibility. If you book through MS, it will be a continuous stay, you will get KTTW for the entire time. If you book through CRO, you will have to go to the front desk and get new keys when you switch to the CRO reservation. Plus that will not be considered a member stay, so no free internet. But the plus side is you get full housekeeping for your CRO nights.