They have a good reputation and I looked into them when booking my trio. The woman who runs it is very sweet. Ultimately, we went with Siena Strings, but they were comparable and we would have been good with either.
I got a cd a few days ago from the Shrewsbury String Quartet, it has 22 different pieces of music on it, their phone number is 609-932-0697. They played somewhere we went, i forget where, so i had them send me a CD.
Re: String Trio...
I know a couple girls that used Heartstrings and were very happy with them and you are right that Susan is very sweet and accomidating. Good luck !