Great in the end, but...
Overall, am very happy with the extra room this product gives me in my partner's 2008 Prius, but one installation issue was a pretty big fail. I ordered and installed both pax and driver side extenders. However, the "B" bracket of the driver side was missing the requisite threading on the backmost seat attachment hole. I also faced a problem with the "B" bracket on the pax side. Apart from the not particularly well-written installation instructions, which were very unclear when it came to the EMS long bolt, (which is not a brilliant solution to begin with) one of the holes that needed attaching to with a factory bolt wouldn't take it. But "luckily" I couldn't use the EMS bolt intended for the non-existent driver side attachment hole threading, so I had a spare, which did the job on the pax side. To resolve the driver side issue, I used a store-bought nut and bolt with washer and lock washer to secure the driver "B" side attachment. One other issue I had to deal with on the pax side was interference from the U bracket. Had to remove it to give room for EMS bracket "B", but needed to trim and reinstall it as nav box was a bit floppy without the support the U bracket offered. In the end, it all worked, but not without some challenges and additional time.