I would have to say go for it. I have an aftermarket warranty that has saved my rear end on several maintenace items. For example intake maifold gaskets, $1700 including labor, covered. One other example would be if you lost an alternator or water pump. I believe both are around $1000 jobs. (Alternator is water cooled and the part alone is $600+).

Just my $0.02

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2013 X5 xDrive3.5i Premium
2002 530I Sport Package
2001 X5 4.4i
2001 M3