The BfV is absolutely not transferable to the US system in any good way. An equivalent would have been under the direct influence of Trump for the last 4 years and its easy to imagine that that would not have resulted in anything good for the American democracy. If anything, it probably would have helped overthrow the government if it was invested with similar powers as in Germany.
What the US needs is not more powerful tools to keep political opponents in check (yes, this is what the BfV is, but is is not immediately problematic because it is constrained by both parliamentary oversight and an effective supreme court), its the already existing bodies excercising their existing tools for oversight more AND the existing bodies to reflect the voting population better. In the medium term, this HAS to include ways for 3rd parties to be viable to get out of the bipartisan gridlock.
Unfortunately, these extremely needed reforms both require an extremely high bar to pass as they would have to be constitutional amendments and they are actively detrimental in the short term for most of the people who would have to pass them, so i expect the American democracy to be replaced sometime in the next few decades.