A few months ago, I posted a detailed report on my long-term experience with my three M&Ps, my Shield 45, my Shield 9, and my M&P 40 compact. It's a long post, so I'll give you an executive summary: The Shield 45 is a superb gun. If you like your Shield 9, you will love a Shield 45. Here's the post:
http://smith-wessonforum.com/140717276-post1.html
My advice is to buy it before someone else does.