I've made these potatoes several times for Thanksgiving & Christmas and it's always been a hit. For my taste, the garlic is a little too strong, so I cut back on it. And I did find it needed a little bit of warmed milk to thin it out. Other than that, I made as directed.
I really liked this and will do it again. It's difficult to press the sweet potatoes through the ricer though, a food processor might be a better choice. The first i made these i had a little bit too much yoghurt, the second time it was much better.