Any memory manager on Windows must somehow get the memory from Windows...
Also their "how to use it" by putting it into the uses... It leaves out some important details.
And the "Lazarus may alloc mem before" is simply wrong. Any code in any app (and completely unrelated to Lazarus) can "use memory before", if their mem manager is incorrectly used. And such incorrect usage is likely to happen because of the vague description how to use it.
Place the SimplySMM unit the first in the "uses" statement.
But not any uses. The "uses" of the "program", and not the "uses" of some "unit".
And also, even better, use the correct command line param for FPC (I haven't bothered to look it up, but IIRC there is one).
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In any case: if it comes with sources => review it.
If not, given the dodgy claims and docs => I would certainly not use it.