Have a play about with a "proper" flash I guess. Use it to take pictures of my little lad and bits and bobs. I've never used one before so probably full auto, but I'm guessing it'll be more expensive for a TT-L?
The big advantage of auto-TTL is speed of use. If you're setting up in a studio or multiple guns outside, then a couple of minutes spent getting the exposure right makes no odds and many people prefer manual in that kind of situation as it ensures the lights stay exactly as they're set.
But auto-TTL really comes into its own when you need to work fast, particularly as flash exposure is very sensitive to distance. It's the inverse square law that says when the distance is doubled the light is reduced to one quarter, two stops down, which is a lot. So if you have a fluid situation or mobile subject, a few feet either way can make a big difference - auto-TTL will track that and keep everything on an even keel.
The other thing you should do is soften the light, which means making it bigger. Various ways of doing that, like a softbox, or umbrella, or bouncing off a ceiling or wall - whole other subject. And you may want to think about balancing the lfash with the ambient light, another subject again.
But one thing I would say is to get at least one good quality gun, the best you can afford, with decent power and also with high speed sync (FP-sync in Nikon speak). You'll need that outdoors in brighter light. You can supplement it with cheaper stuff as and when.
Having looked at it, the Jessops one might be better for me as it claims to be "Dedicated TTL flashgun for use with Nikon Digital and film cameras with a TTL hotshoe."