Before buying the Duke, I had looked though many of the reviews here and elsewhere. I say many of the reviews that complained about the Duke falling out and other such issues. I ended up buying it anyway since the general consensus was positive.
I have not had any issues with the Duke staying in place. The vibe that comes with it certainly could be stronger, but it is still more powerful than most of the none-wand vibes I have seen. I would have to agree with other that the Duke is probably not going to do much for experienced people. Someone with good knowledge of their body will most likely be able to hit the right spots more effectively themselves than the Duke can. It is still a convenient option none the less.
After using it I would also not say it would be the best toy for someone just starting out either. While the circumference is reasonably small at any given point, some sections will still be too big for some people that are very new. This will also be affected greatly by the angle used when inserting.
I would say the Duke is the best fit for people that have low-to-moderate experience with anal toys. Someone that has already used small-to-medium sized toys will likely not have any trouble inserting it. The Duke definitely provided an enjoyable sensation for me and would be fairly easy to insert for this type of person. I would also say that the Duke would be good for people that haven't intentionally tried prostate play before.
As for the Build of the toy itself; I would say that it is good quality. The silicone piece of the toy is made from a very good quality silicone. This is especially useful for people that have multiple partners that they want to use it with as it can be sterilized (make sure to follow the directions for that part).
The vibrator is of decent quality in my opinion. It is made from a hard plastic and is sturdy, but also has some of the issues associated with plastic. For example, the seam where the pieces are combined is pretty rough though less rough than a cheap plastic vibe. This does not have any real downsides when using it, but I do find it visually and texturally unpleasant when cleaning it. This also makes it harder to sterilize on top of the fact that it is plastic. Personally I wish they would use a metal construction for the vibe as that would have a better texture and be easier to clean thoroughly. I also think that a metal design might dampen the vibrations less than plastic does. The controls for the vibe are pretty standard, so there is nothing of note in that regard.
Overall, the Duke is a much better quality toy than many of the super cheap toys that are around, but also wasn't some kind of life changing product. I'm not sure why some people expect some thing like this to be life changing but I figured I would make note of that to temper some people's expectations.
Hopefully the detail here can help you make the right choice. Even though I have other toys that I prefer; I still have zero regrets in purchasing the Duke and expect to get a good amount of use out it.