Honestly I wouldnt suggest using these shakes as your only source of nutrition and then later adding real food into your diet. I would balance the shakes with at least one meal (and possibly snacks) per day.

First of all, the energy your body would use to metabolise these shakes would be drastically lower than what would be expended to digest fiberous vegetables such as broccoli or spinach. This means that your Basal Metabolic Rate (BMR) would drop so you would have to actually take in even less calories than what MFP tells you to eat per day. Overall it may not be a large amount, but there would be the difference.

Secondly, you also have to take into consideration that for the time you use only the shakes your body and metabolism will adjust to that as fuel. When you start adding regular food, you may end up bogging down your metabolism, thus slowing your weight-loss progress.

A balanced diet would be more beneficial and you would be developing good eating habits in the process.

This is only my opinion.. I am not a doctor, but you really should consult one before altering your diet to this extent.

I have not tried them but you will have to let me know how they are..