Latest update from a Mown3r of a 2017 Mazda3 Speed HB. The most glaring issue is with the Motolite replacement EFB acid leakage. Quick tip: always do a weekly checkup on battery leaks!

Despite a liberal application of duct tape on the Enhanced Flooded Battery (EFB), the replacement Motolite battery continues to leak or vent out corrosive acid. This is evidenced by the labels on the battery almost turning black on the edges, and even more worrisome is that it’s starting to eat through the metal battery tie-down. It’s become so bad in places that the battery tie-down has almost been eaten through.

Although we cannot confirm why this is happening with the Motolite battery, a quick Google search reveals that owners have been complaining of the battery’s poor construction. The plastic, they say, used on the battery case is thin and prone to cracking. For example, an overly tightened battery tie-down would be enough to cause small cracks, enabling corrosive acid to vent out. Although the damage is so far limited to just the battery tie-down, we’re hoping Mazda Philippines would be replacing the battery and battery tie-down for safety reasons.
Overall the Mown3r seems to be happy with the M3's engine performance and fuel efficiency.

The article also mentioned about the "visible" engine hood insulation that can be bought separately:

Interestingly, the Mazda3 integrates its engine insulation into the plastic engine cover saving weight and cutting assembly complexity in the process. However, if you’re a bit OC and feel naked without seeing an engine insulator installed, you can actually get one specific to the Mazda3. Designed for the Skyactiv-D variant, you can order the hood insulator (Part # B45A56681), 10 hood fasteners (Part # TD1156694), and the rubber protectors (Part # GHP9-56-9Z1 for the left and Part # GHP9-56-9Z2B for the right). Not only does it make the engine look “more complete” it actually does makes the engine seem quieter. And given our problem with the leaking battery acid, it also offers additional protection (better the hood insulator than the hood itself, right).
217 Mazda3 Speed: Long Term Test Update # 4 | Philippine Car News, Car Reviews, and Prices | ************