I also have a Mantus anchor.
It seems to work very well! No issues yet.
This weekend I thought I had a first issue, but I had someone on my boat manning the windlass that didn't quite know what he was doing, and he hadn't let out enough line. The anchor line was hanging almost straight down, so I don't know if the anchor was even fully touching the bottom yet. It was very windy and it took 3 or 4 tries before I finally said "let out a lot more line", all of a sudden it grabbed so hard and quickly that you could hear the anchor line creak as it stretched in the wind.
I did end up with one size too big for my boat. I have the 45 lb Mantus, and I think the 35 lb would be more than enough for my boat on our lake. So if anyone has a larger boat and would like a 45 lb galvanized Mantus, I'll save you some money, just purchase the 35 lb version and I'll swap with you.
For my boat size, the 45 lb is considered a storm anchor. This is the size where you would set if you were overnighting on the ocean and a storm could pop up, and you didn't want to worry about the anchor losing hold while you were asleep. Considering that we can never overnight on an anchor on our lake, there is no need for such a large anchor. Now if someone had a 35 to 43 ft boat, this may be a good anchor for you.
But overall, I'm very happy with the Mantus.
A dock neighbor of mine researched it also, and ended up with two. One as his main anchor and another much smaller one to use as a stern anchor. He felt the stern anchor was a good choice, as often the one he was previously using would be hard to get to set and also would break loose sometimes.