I have 2 extra lights for reading when I don't have my preferred Sony lighted cover with me.
I love the
Verso Arc Light, it fits very nicely on top of the reader with the Sony non-lighted cover. You'll have to see if you have enough free space along the top of the reader to attach it with your cover on though, the shoe needs 1-1/4" free from the cover in the middle. I love that it's rechargeable, and it uses the same USB connection as the reader. It lights up the reading space evenly and no glare spots.
I also have the
Might Bright Travel Flex for my 350 and it fits great with a cover. I attach it to the back flap that's turned under the reader while you're reading, and twist the neck so it's really sideways across the top of the reader and it also lights up the reader very well and evenly, no glare spots for me. I also like that it only takes one AAA battery.
I don't know how either one could attach with the silicone skin on though, I think the clip wouldn't be able to attach to the full thickness of the reader and skin.
As far as how securely they attach, if you turn the reader upside down and shake it, both would probably come off, the Verso quicker than the Mighty Flex. But I certainly don't have any problem with them staying on as they should just while reading.