PhoneArena has looked at the HTC HD Mini and have published their usual thorough review.
They score the device 8.5/10 and conclude:
So is there a reason why you should get a Windows Mobile 6.5.3 handset with Windows Phone 7 coming at the end of the year? Since none of the apps for the current-gen Windows Mobile phones will not work on Windows Phone 7, we believe users should have no hesitations when getting a WM device now. Looking at the existing crop of smartphones running this platform, we have to say the HTC HD mini is a perfect choice, due to its ease of use and reliability. Right now, the HD2 is the undisputed king of Windows phones, but if you’re not really into such great sizes, the HD mini is just for you.
Read their full review here.