It depends what's in the shake. If it's fully balanced and highly absorbable, so all that nutrition is going directly into the cells, maybe. If it doesn't have 70+ ingredients and some of it is eliminated, then it's not going to keep you satisfied. The body goes into starvation mode and the metabolism slows down, which means you burn fewer calories. Most "diet" shakes contain stimulants which are not at all good for the central nervous system (and a lot rely on caffeine), and most protein products don't have the right balance. If they are pre-mixed liquids, forget it - the proteins break down while the product is sitting on the shelf, so it's not giving you as much energy.
It also depends on whether you're going to be "mentally" satisfied by a liquid shake or whether you're going to crave something to chew. A lot of times a replacement shake doesn't feel like a meal, and in an hour you want more, both psychologically and because the nutrients didn't satisfy you anyway.
The protein bars are no better - most have a lot of sugar in them. Even if they say "no sugar added" it can mean there are already sugars naturally occurring in the ingredients, or there are a ton of chemicals to "offset".
I wouldn't buy anything commercially available at a vitamin superstore like GNC or even the supermarkets and gyms now - they have so many options there that you'll grab something and they'll make money no matter what you do.
I'd also be really concerned about where the product is made and under what conditions, since the industry is not well regulated. A lot of companies just jump on bandwagons and throw in the latest fad, more concerned with profits than your welfare.
I've only seen one meal replacement product that is based on real food science and that's from a company that gives your support and consultation. That's based on cellular nutrition and getting the ingredients directly into the cells.