Its a little large for a Micro. It's also a lot more ESC then you will ever need for a Micro. The specs on duratrax's web page states that its a good sport level ESC. Keep in mind that they are talking about 1/10 cars and trucks.
Sounds like your LHS just wanted to sell you what it had. Unless you got a really good price on it, a much better choice would have been the Futaba mc230. Its smaller, inexpensive and can also be used on your 1/10 stuff later.