You can download the full plugin directly from the developer and use it for free for a limited time (usually 14 days) to test it out.
So, putting this all together, my response should inform them that the full version isn't free, provide a link to the official MFB site for purchasing or demo, suggest alternatives if they're looking for free synths, and warn about unsafe sources. I should also mention the types of sounds Iron Axe offers, like analog warmth, to help them decide if it's worth purchasing. iron axe vst free download link