A customized notification light is infinitely better than Glance. As I said in the other topic, you need to be close to Glance to see it. From more than a few feet away it'd be hard to tell which inbox has email, and from 10 feet away good luck telling anything much. If you're close enough for Glance to make sense, you're probably close enough to give the phone a quick squeeze and see if anything needs attention.
A custom notification light gives you all the info Glance does, but can do it from across the room. It's so much more powerful than Glance it isn't even funny.
Once I got rid of a notification light (something I never thought I could do without) I decided it felt more like a nanny to me than anything useful. It became a nag. And, with work email on my phone, it was an especially hard way to tune out, because it would constantly tell me I had work email to check. Without it, it's much easier to just check out of work for a bit and check in when I want to. If anyone needs me, they'll call. For all those emails, I'm happy not having the constant blinking.