I got on absolutely brilliantly!
I took out the broken 6-CD changer from the glove box of my 2002 RX 300, and replaced it with a Grom unit from http://www.carputer-shop.co.uk/usb-car-kits-c-7/toyota-lexus-usb-mp3-integration-kit-p-47 I needed the TOYF cable to act as an adaptor to the plug that I pulled out of the back of the CD changer, and the whole thing just worked. Sound quality is better that CD, I'd say, and you can copy as much music as you want, just about.
A (very) minor niggle is that not all the buttons on the display work, but random does, and that's about all you need. I used sticky-backed velcro to hold the unit to a base behind the glove box, through the hole left by the CD changer, where I can reach the USB stick for whenever I want to change the music.
Total cost about £120, I ordered on Thursday, it arrived Friday, and was installed Saturday. Brilliant!