There actully very comfy I think, I drive around 50 round trip each day for work and haven't had a problem
Only thing is I haven't sat in many other seats so I can't comment on others. I chose these tho becuase they have great reviews on here for being cheap, supportive and comfy, which they are!
I don't have them on sliders no, just fixed to OMP side-mounts and then fixed to OMP subframes which is then bolted to the floor. Check out my project thread for more info.
Also if you buy them from the company on eBay "ralleyshop.pl" who are the main distributors for these seats, then you'll save yourself £100 a seat from what "seats4u" sell them at. Deliver iis quick to at around 3 days.