Zed vs Shen decks, how to tinker?

Hello! As said in the title, I’ve been thinking of buying the Zed vs Shen decks, I want to get into playing as fast as I can and I’ve opened a lot of packs but most decks that interest me (like Mel and Kennen) seem to have a couple cards I find too expensive to splurge on now since I don’t actually know if I’ll like them or not. None of my bulk is enough to form an actual deck yet.

Are the Zed and Shen deck worth it? And most importantly, how have people been tinkering them to make them better/more competitive for local tournaments?

(Psa; I’m not looking to win or be super competitive at tournaments, I’m just a beginner but I’d like to have a decent deck so I’m not completely hammered on the first go.)