If you don't have an oversized handlebar, then how about a
Planet Bike Insight 15W. I'm getting one for my little sister.
It has high/medium/low settings, plug-&-forget smartcharger, and a battery that fits a waterbottle cage. Yeah, it's a little more money than your $60 HL500/HL300 proposal, but you won't have to keep buying batteries, and it will dominate the LED lights in letting you see where you're going.