No, really. They are. I love slow cookers.
People like to tout these as great things to have if you work a lot and want a meal ready when you get home. Well, if you live very close to where you work, it's doable but I work over an hour away from where I live. So I won't be letting a meal cook in the slow cooker for 10 or 11 hours. That's just not going to happen; I doubt the meal would be edible. If you have a timer (they are available, and some models have one built in), you can set it for the cooking time and the cooker will switch over to warm when it's done.
I have a couple of basic, manual models and I give them quite a workout on the weekends. First, you can quite comfortably leave these things unattended for several hours, so I can run errands, clean, do laundry, or hang out with my friends or family if they are over for dinner (this is really nice--you don't have to rush around and get dinner ready; you can actually talk to your guests. Amazing, I know). They cook food at such a low temperature that you can literally set it and forget it. It makes the toughest cuts of meat very tender, so you can buy more inexpensive cuts. And it uses far less energy than your stove or your oven, which is a plus. They also do not heat up your entire kitchen the way your stove or oven do, so they are actually quite useful in the summer.
They aren't just for stews, though they are great for that. If you want to cook an entire chicken but don't want to heat up your entire kitchen by turning on your oven, the slow cooker is the way to go. If you want to make pot roast, the slow cooker is the way to go. It's great for if you want to make chicken caccitore, chicken a la roma (which you serve over pasta) or other dishes. And you can do vegetarian dishes in the slow cooker--chilis, beans, curries. . .pretty much anything. Even dessert.
If you can only get one, and you eat meat, then I'd get an oval slow cooker, at least four quart sized, maybe six quarts. You can easily fit a chicken or roast in there and you can still do soups, stews, cut-up chicken, chilis, and other meals. You shouldn't pay any more than $25 for it; and they often go for less. Yes, you can get more expensive models with all sorts of bells and whistles, but it's kind of weird to have a tricked out slow cooker. It's a slow cooker. The point of these things is to save money by cooking at home more, and cooking inexpensive food like tough cuts of meat. It's like making mac and cheese with some fancy, expensive artisnal cheese. Um, it's nice but come on. It's mac and cheese.
If you decide that you'd like another one, then feel free to get a round one. If you want a round slow cooker, first take a look in thrift shops, white elephant sales, and yard sales. Someone is always getting rid of one. The older versions do not have removable crock inserts; they are all one piece. I have two slow cookers; an oval six quart one that I got for Christmas years ago and a very old, round four quart one I got for $5 at a yard sale. I use them both quite a lot. (I had friends over for dinner today--I made dinner in the 6-quart and dessert in the 4-quart.)
Cooking with these is quite different from cooking on the stove top or cooking in your oven.
First, remember spices. If you want to use fresh herbs, you'll need to put them in towards the end of the cooking time; otherwise the herbs will cook and lose their flavor over the 4-8 hour (on average) cooking time. Most recipes call for dried herbs for good reason.
Second, remember to keep it covered. The slow cooker works by cooking food at a low temperature for a long period of time; one way this is accomplished is by keeping the lid on--the heat and the steam doesn't escape. It's tempting, yes, but don't take the cover off unless you absolutely have to.
Third, remember to add a little liquid, but not very much. Because it cooks at a low temperature, and because the moisture in the food and that you've added will not escape if you leave the cover on, you don't need a lot of liquid. You need some to add some steam heat, but not a lot.
Fourth, remember your medium. Because you're slowly cooking something in an appliance that keeps the steam and moisture in, do not expect, say, crispy skin on your chicken. In fact, if you decide to slow cook an entire chicken in your crockpot, be very careful when taking it out. It will be so tender that it will fall apart. (This happened to me once, and my then roommate was cracking jokes about angry, exploding chickens that were resentful about being our meal. But as I pointed out, angry exploding chickens are delicious.)
Another thing to remember is that dairy doesn't do well in the slow cooker; it breaks down over long cooking times. The only exception I've seen for this is macaroni and cheese, and even that calls for processed cheese along with cheddar cheese, and that only takes about two hours to cook in the crockpot anyway. You'll notice that instead of a white sauce, creamy slow cooker recipes call for cream soup to be added. Most dairy is added toward the end of the cooking time (sometimes evaporated milk can be added.)
If you want to know a real expert on slow cookers, you should visit this blog. And if you haven't tried one out, I'd advise you to. They really are great.