It's still an extremely risky thing to do. These kind of letters have legal value, any formal error can open you up to getting your demands rejected (and there's no plan B, the moment they find a way to get out of paying you legally you're effed up), postpone the payments indefinitely or other issues.

Don't do a lawyer's job unless you're a lawyer, because the guy on the other side will definitely get the best lawyer he can afford to retain as much of his money as he can