Here’s the secret that cookware companies don’t want you to know: Temperature settings vary wildly. Some slow cookers run hot, some run cool, regardless of brand. So your “low” might be my “medium.” That’s why your friend’s pot roast is perfect and yours is a sad, gray brick.
Solution? Buy a cheap oven thermometer and test your device. Boil water on low for a few hours and see if it simmers. If it boils, you’ve got a hot tamale. If it barely whispers, you’ve got a sleepy one. Adjust accordingly, and you’ll be fine.