Quality will always win-out. Still, there is a percentage of clients that always shop price and allowing a competitor a foothold, allowing them to have their equipment seen in the neighborhood has got to give any small-businessman pause.
A non-compete is valid if it is not too restrictive. In other words, you can have someone sign a promise not to solicit business in a narrow area--say a section of town--but cannot restrict them from a total city, state.
Whether or not it would be worth the costs of litigation is difficult to know. Still, strictly from a practical point-of-view, a non-compete might be a decent insurance policy.
Do you think that asking employees, after they've been hired and on the job for a number of months, would cause ill-feelings?