^^
i bought a set from pepboys earlier this month to do my radiator flush. im lowerd on tein stech... i had to use boards to get up. but these where well worth the $35 i paid. i have to drive on things just to get a jack under the front now anyways. but these ramps where prolly the best thing i bought in awhile to use to work on the z. made my life way easier. i have the 12k kind.
also the issues with slipping could happen with any ramp... it comes down to user error imo