I bought the 6mmRem reamer this year, 2015, and built a rifle on a 1903 Turkish mauser action with a Douglas 12" twist barrel.
It did not shoot well enough to hunt.
I may revisit it with another barrel.
It is going to burn out barrels if you hunt rodents with it.
1000 rounds probably max.
I bought a 6mmXBR Krieger take off barrel that had wear.
I bought an old Rem700 22-250 that had barrel wear.
They are no more overbore than a 7mmRemMag, but those don't get 1000 rounds fired. The low recoil of the 6mmRem can allow it to get burned out.
So I would look for a used one owner with a known rounds count.