I found Tangible Software Solutions to be very easy to work with.  In the course of my review I had several questions and found one bug.  All of the questions were answered quickly and the bug was fixed the same day (a Saturday!) I reported it, with new versions of the applications immediately posted to the web site for download.  I was quite impressed with the level of support and responsiveness I received.

I also learned in the course of working with TSS that they heavily test the products using both private test suites as well as publicly available examples such as the 101 Samples available on MSDN (in both VB and C#).