Hi Kathryn
Between a bar and a shake the difference is only 30 calories, so there isn't a huge difference. I don't think you would lose more weight...but I could be wrong!
If you are getting sick of them, why not have less a week and 'save' them so they are more of a treat? When I first started I used to just have bars at the weekend (but I love them too much so that didn't last very long, haha!)
xx