I've found that a lot of meals done via the slow cooker tend to taste the same because of the consistently and the type of ingredients typically involved in them.
1.) My hi/low setting probably doesn't match your hi/low setting. From the get go, we're cooking the same meal at two different temperatures.
2.) A lot of recipes seem to call for low setting for 8 hours. This works well for a lot of people with a standard American work day, since a stew/soup will stay above safe warming temperature in a nearly sealed pot. However, the cook times are too long. Thawed chicken for 8 hours on low almost never turns out with the right texture. In this case, it's convenience > taste.
3.) The flavor is cooked out of the ingredients, and/or there isn't enough seasoning or too many ingredients. When you get the seasoning right, too long of a cook time can dull the flavor. When there isn't enough seasoning, then your meal is bland from the start. When there are too many herbs and spices, you get a mish-mash of flavors that are all competing for attention. There was an article on here a long while ago that categorized foods into low and high amplitude flavors. Something sharply distinctive was high amplitude (think nacho cheese Doritos), while a low amplitude food had weak, hard to discern flavors (plain grits). Too many different ingredients can lead to low amplitude foods, and when I see an ingredient list with 15 different herbs and spices, I almost always steer clear.
While it does double as a slow cooker, I have never actually used that functionality.
Sous-vide much more specialized, but I find super useful not for saving time, per say, but being more flexible about it. It's great when you are doing other things at the same time as cooking dinner, i.e. - leave the steaks another 30 min while I do this chore? no problem....
