For streetlit roads I’d edge towards the Cateye Holy Hand Grenade thing. Very visible from front, back and side. The bracket isn’t great – mine bounced out as the retainer broke, the one on my Roadrat it’s now glued in with No More Nails so can’t take it off without unscrewing the bracket (though that’s a minor hardship I guess). Good that you can have one row on constant and one on flash too.
The Exposure Flare is very good indeed, amazingly tiny and bright, sort of casts a pool of light behind you on unlit roads and the flash mode is a constant light with a bright pulse every second which I think is very visible. Decent side vis, and about the size of a champagne cork and weighs alomst nowt. Can’t say much about battery life as not had it long enough, but I have the rechargeable so reckon charging up once a week will see me right.
The Mars 3 is OK but mine doesn’t seem very waterproof – seems to let rain and spray in very easily. Fortunately it still works but seems to only go on constant mode and eat batteries even quicker than normal.
Don’t know about rack mounting for any of them, sorry…