Hi there, I don't own an IS, I own an NX 300 and purchased my roof racks from my Lexus dealer. The roof racks are easy to fit, only take about 3 minutes to attach and same to remove.
All I can say is I am so thankful that they are so easy to attach and remove, simply because they are soooo ugly on the car 😞 I was sort of hoping I could leave one on for attaching a UHF aerial to, but nope too ugly. So if you looking for something that looks good on your Lexus, you might want to look at them first, as I got mine in the box and never saw them until first time I attached them.