I just purchased a platinum bumper-to-bumper exclusionary EW from Mercury for my 07 650 which ends the factory warranty in Sept. Mercury rates the 6 series very favorably (compared to 3, 5 and 7 series), so the 6yr/75k mi policy only costs $1.9k plus $200 (elec package for iDrive, heads up, and night vision), and $250 (reduces ded from $250 to zero). Part of the reason for the favorable price is that my 650 has just less than 30k mi on the clock.
Mercury's been around for a while, and they get high marks from my SA. My one concern is that, unlike the Great American exclusionary policy on my 535, Mercury excludes injector failure. But this is not a major concern on the NA 650 as opposed to the direct injection 535 which is prone to injector problems.