FWIW, i have the Schroth Rallye4 (like the one in the initial post, but with two rear mounting points) and it works really well. it was easy to install and didn't require tapping any of the seat belt mounting points...it re-uses all of the OE bolts except one, for which they provide a longer replacement bolt.

 

Mike - Do you remove the rear seat? Do you have a roll bar installed?

 

nope, neither. the rear section of the harness bolts to the seat belt anchors and comes up around the sides of the cushion. the front section fits through the hole in the front headrest and can be detached from the rear section. for daily use i detach it, pull it back through the front seat, and drop the sides of the harness around the sides of the front seat.

i use it only for autoX; if i do a track day i might just use the OE seatbelt. but it works really well for autoX.