The primary way to obtain a "solid piece" of Metal Slug on PlayStation 4—referring to a compiled installation package (PKG) or physical release—is through Metal Slug Anthology
This anthology is a compilation of the original arcade run-and-gun titles. PlayStation Store Included Games Metal Slug Ps4 Pkg
Online Trophies: Earn achievements for completing difficult missions. The primary way to obtain a "solid piece"
If you are looking for more specific information, I can help you with: Cause: Missing licenses or conflicting HEN payloads
For the average gamer: No. The official ACA NEOGEO releases go on sale for $3.99 regularly. They run flawlessly, support trophies, and require zero hacking.
If you are looking for a physical "solid piece" for your collection, there are specific limited releases: METAL SLUG ANTHOLOGY™ - PlayStation Store