Which camera slider ?
 

I got a skater dolly for my wedding movies and I faced two big issues. It could not be used in outdoor events , as the surface is not even like the tiled floors.

Also, it can only take bottom or top depending on the support table.

So I started looking for a Camera Slider.

I found this two good and cheap,
Amazon.com: StudioFX 40" Pro DSLR Camera Slider Dolly Track Video Stabilizer: Camera & Photo

and

Amazon.com: JRFOTO Camera Track Slider Camera Silder Video Slider 32" With Ball-Bearing Slide Mechanism By JRFOTO JS32: Camera & Photo

Which one do you recommend ?