The main character, named Lugh in his reincarnated form, maintains the memories of his previous life, and so from a young age already demonstrates extreme proficiency and potential. OP main characters are not always bad, but are better suited for parody/self-aware isekais such as The Misfit of Demon King Academy. When the show takes itself even remotely seriously however (such as this one), it becomes a bit of a drag to watch a character that knows and can do anything, always.
Beside that, while the formation of harems seems inescapable in this genre (for the most part), this one felt especially gross since our MC is basically a guy in his 50s inhabiting a 14yr old's body. The worst offenders are Maha and mostly Lugh's own mother. Maha just meets this guy and immediately refers to him as "my prince." Lugh's mom wants to see his pecker and talk about ejaculation. Maha at least was an interesting character at first, but loses the edge when she joins the harem. Somehow, with these atrocities, the later scenes with Dia and Lugh managed to be properly infectious and adorable, and I enjoyed every moment she was on screen.
The other main pitfall would be that the anime doesn't seem to know how to spend its 12 episodes. It was interesting to see the main character develop from childhood, but again, with just 12 episodes, it was an arc that, along with his journey to become a merchant, took entirely too long. By the time the story returns to its main thread (kill the hero), there isn't much time left, and the final episodes feel incredibly rushed. It seems as if they paced the first 8 (or so) episodes as if they had been given a 24-30+ episodes budget and had to turn things up to 11 when they realized there's suddenly only 3 left.
In conclusion: not a waste of time, but frustrating at points along the way, and the best parts to take away from the anime are the moments Dia is on screen. Had there not been the weird harem and odd pacing, this would've been an easy 7.
