I've found eBay is a good option for Cygolites. I've got 4 on my bike. All from eBay. All really cheap (but new and working)
I have the Hotshot 150 on the back and the 460 Dash up front. Those are my primary lights. Both can be seen easily in the middle of the day with the sun behind the light.
Then I have 2 Hotrod 50's (white up front, red in back) as secondary. Both would be more than adequate by themselves at night. In the daytime they are under powered BUT they can be seen from the sides better than the Dash and Hotshot which are much more directed straight way from the light.
As for the Hotshot mount....I have 2 mounts. I rigged a custom mount on my commuter that hangs from my trunk rack. I used the original clip part but mounted it to the bike my own way. It works fine. I have the standard seatpost mount for my other bike which I use upside down because it positions the light better under my seat bag. Even upside down that works just fine. I have no fears of the light falling off.
In the winter when I commute in the dark I add 2 cheap USB chargeable white lights to the top tube, aiming down and slightly out. This lights up the bike and the ground below me. They aren't super bright but they make the bike glow like there is a spotlight above me. Makes me easily visible from the side with this big light spot going down the road.