I've used heavy cream to go from about 140ish lbs to about 215lbs. It definitely works and can work fast. BUT, and that's a big but (ha!) It still takes time. 1 quart of heavy cream is about 3600 calories. Which if it all converts to body fat would be 1lb. But, you still have to eat your daily 2000-2500 calories on top of that. Also, heavy cream being so high in fat it can take your digestive track days to week or so to adjust. Even then it can only digest so much. Drinking smaller amounts, a few hundred calories worth throughout the day can help.
Delayed weight does happen. But I've never noticed it to be anything crazy. Usually just noticing more jiggle or a little bit more of a roll forming. It all depends on how much you gain and how much you weight already to see if it's noticeable. Weight gain in general is a marathon not a sprint. I will say, if you keep using heavy cream as the weeks and months the pass you WILL gain a lot. Keep at it