Skate board ramps for bashing?

[JThiessen]

I've been toying with the idea of buying several of those plastic skateboard ramps.
There are these for 8 bucks each: http://www.sears.com/shc/s/p_10153_1...9110000P?mv=rr
Or these at K-Mart: http://www.kmart.com/shc/s/p_10151_1...8110001P?mv=rr

Anyone use them? Do they hold in place fairly well? Is the one from sears good for backyard racing, or is it more of a trick jump thing? I'm more inclined to grab the style that K-mart has.