Cateye Holy Hand Grenade (see Snakebite's pic) is too wide, can't easily be mounted at 90degrees, and is heavy with 4x AA
It takes two AA batteries not 4. No it's not easy to mount vertically if thats what you mean but then again that would make the side led's pretty pointless. And I've not found the width an issue.
I use a combo of lights on the back - one Cateye TL-LD1100 (as pictured above) on my seatpost one row flashing and one constant and one on my camelbak one row flashiing and one constant, one fibreflare on my driveside seatstay set to flash, one cheap flashing light under my seatpost, one on my helmet and one Cateye SL110 on the shoulder strap of my camelbak. Yeh I'm lit up like a christmas tree but I am visible.
If you have lights on your offside then drivers generally give you more space.