Could I use the scout as a primary during a night dive?
Ye gads, this is a tough one.
Outside of the DIR forum, I'd give this a resounding YES! A 3W LED scout is as bright as any cheap light on the market, and if you buy one (or two) then it's not money wasted.... you'll never get your money back on a cheap light that you flick on to some suck who doesn't know any better.
I've used just my 1W scout lights for cavern, wreck and night dives....... no, you won't be able to really signal your team with them in the same way as a 21W HID, but they are bright enough to see by and nice robust lights. A 3W would seem a nice compromise for now, that you add to later.
Of course, this is the DIR forum..... so I won't say any of that, you should of course by a decent primary from the outset.