I would need to know the nutrition facts to compare them. It doesn't make any difference if you mix the powder yourself (with water or calorie-free beverages such as crystal light, depending on the flavor) or if you buy the ready-to-drink shakes. I recommend comparing the calories and carbohydrates. As long as you get around 20 grams of protein and stay within 5 gm carbohydrates per meal (or in this case, per shake), then they are acceptable.
I am a little concerned with you using them for 2 meals/day x5 days/wk. That's great that you are losing weight since your appointment, but if it comes to a hault, you need to eat solid protein instead. There are several options for convenience such as string cheese and deli turkey slices rolled up, or a tuna/chicken foil packet, or even cottage cheese or Carbmasters yogurt w/ 1/2 scoop protein powder mixed in it. Boiled eggs are easy if you like them. If it's working for now, then I'm glad you are staying on track, but in the long run, you may plateau by doing that or you may start getting hungrier between meals.
Pam Helmlinger, RD, LDN, CDE