W164 M-Class as a used prospect

[muchacho]

I am looking to relieve my 190E 2.5-16 of a few family duties. Having already test driven a new GLC I can attest to the serious merit of that car but I am likely to get the option of a 2010 M-Class - specifically a 350 CDI at under 50k miles. With the attraction of buying outright what do folk reckon about these W164s? A considered alternative would be an "old" Audi Q7.