I have never used the shakes (the idea makes me gag as I am not a milk drinker) but I use the bars. Since I am always on the go for work I had trouble staying away from fast food at lunch time. Now I grab a lunch bar before leaving the house and eat it in my car as lunch. I also eat the snack bars for the same reasons. I love the taste of the bars so choose them over some of the other brands out there. It's not a "diet" but rather a convenient and easy way to avoid overeating during the day. Oh and the snack bars are very useful for those times offices have doughnuts or cake on offer - much better for me to have a slimfast snack bar.
I have tried packing lunches but they go bad in the car in the sun or I forget or do not have enough time in the morning or forget to buy stuff or ... the list is endless and always end with me starving and buying something bad.
I stock up when I have coupons or they are on sale and compared to buying fast food they are very cheap! Although I wonder what the cashiers think when they look at me and at my million boxes of slimfast