I can't speak for every chelator, of course. I can only tell you what I've read from people who chelated with their fillings in and had serious problems because of it.
The chelator you mention contains ALA and cilantro, both of which could pull mercury from fillings. I don't want to say the company is necessarily lying (I haven't tried their product, so I could say that definitely), but their claim is highly suspicious. It wouldn't be the first time I've seen an extremely dubious claim in an advertisement.
I usually try to err on the side of caution when I see something so suspicious.