I have a 5 mWatt which is plenty, in my opinion. It is fine even in the bright sky of Melbourne suburbs.
Here's a recent thread discussing use of a mounted laser:-
http://www.iceinspace.com.au/forum/s...ad.php?t=25313
Search and you'll find more good threads.
Here is a description of how I use mine to point the scope, from a previous thread:-
"I have also perfected the use of my green laser pointer as a finder (after watching Ken use his in this way). A wedge of wood, glued to some fridge magnet pieces, sits between my finder dovetail bracket and the focusser base. I have adjusted the finder bracket to be completely parallel with the focusser base. I can place my pointer neatly between the focuser base and the wood, and the projected beam clears the scope body and “spots” the sky almost in the middle of my 30mm eyepiece (suggesting my optical and mechanical axes are well aligned?). Move the scope until the end of beam is in vicinity of target and check in the eyepiece that I have it. Then pointer goes back into my top pocket to keep it warm and functioning for the next target."
Now, the bad news. Go to your State Government website and search for the list of prohibited weapons. In Victoria, you will find that a "hand-held battery-operated article" that emits a laser beam "greater than 1 mW" is a prohibited weapon and certain licensing requirements exist.
If you get one, I recommend that you, 1) be very aware of the presence of aircraft in the sky, and, 2) don't let a child (or childish person!) get their hands on it regardless of how much they plead with you.