VFM-9 question

So as an impulse buy I grabbed a VFM-9 5in upper plate last night. Now, I saw the "COMPATIBLE WITH 9MM GLOCK STYLE MAGAZINES" warning before buying and was hoping I could play fast and lose with that for my elderly LAR-9 Colt lower. But after sleeping on it and actually doing some post purchase research my question is, how effed am I?