I didn't have much confidence in the seat post mount for the Cygolite Hotshot 50, or the plastic spring clip built into the light. The plastic spring lacked stiffness and had no backup latch. To minimize the risk of the light popping off on a rough road, or being easily stolen, I set the light's seat post clamp mount high enough that the saddle interferes with detaching the light. I can still recharge it since the USB port is located at the bottom.
I wouldn't trust the Cygolite Hotshot 50 clip on a typical saddle bag fabric mounting loop, or pretty much anywhere else. I'd first want to reinforce the clip with some heavy duty Velcro to lend a bit more grip.
Blackburn's current to-be-seen safety lights have the most secure spring clips I've seen. Not the older Blackburn metal spring clips (those popped loose easily -- I retrieved one during a group ride several months ago and gave it to another cyclist when the owner didn't claim it after a couple of months). But the newer stiff plastic spring clips used on the 2'Fer and a couple other lights. The plastic spring clip is quite stiff but durable and hasn't broken after more than a year of regular use, including unclipping to recharge (it's difficult to recharge the 2'Fer while mounted on the helmet or bike). It has an inner protrusion that latches stubbornly onto the provided rubber band mount, and a second smaller lug that helps minimize the risk of popping off a fabric loop on a bike bag.
The Blackburn 2'Fer isn't quite as piercingly bright as the Cygolight Hotshot 50, but that's in part because of different designs. Cygolites use lenses to concentrate the brightness into a fairly narrow aperture or angle of view, which somewhat compromises the side visibility. Blackburns omit lenses and use clear protective housings so the lights are approximately equally bright across a wide angle of view from behind or to the side. Not better or worse, just a different design approach.