Mezlan is a Spanish shoe manufacturer--undoubtedly one of the largest in that country, if not the largest. Their shoes are generally of good quality and tend to sell in the midrange sector of the market. They're often discounted by online sellers. Actually, their shoes vary considerably in price, with their lowest-priced models selling in the lower end of the Allen-Edmonds range, and their higher-priced models in the $700-$800 USD region. I believe that their shoe collection manifests several construction methods--with some welted and others Blake-stitched or possibly Blake/Rapid. Their designs range from the conventional to the really exotic, with some almost over-the-top, "fashion-forward" models. Their more expensive models can have more than one color included, mixtures of smooth leather and suede, unusual design features like double seams and such, and, most of all, use of exotic leathers like croco, alligator, ostrich, stingray, and eel. Eel, anyone?!
They stress comfort in their advertising; thus, with a break-in period, yours might become much more comfortable than they are now. It's possible, however, that the last on which your shoes were made is just a poor match to your foot. Still, even with less-than-ideal lasts, most shoes do become reasonably comfortable after wear. As for what appears to you to be a plasticky finish, it's possible that your particular shoes were made with corrected-grain leather. However, I doubt it. They may just be finished to a high shine. If, on the other hand, they are corrected-grain, then no polishing or leather treatment will change their plasticky appearance.
If you like the appearance of the shoes, why not see how they do after breaking-in. You might be pleasantly surprised. If you're pretty sure you don't want them, you could see whether a return is possible. If not, give them a chance. If they still don't impress you after breaking in, eBay is always an option. Good luck.
