Not sure about the backlight as I was not interested in hooking it up, you can tell they are yellow when off. However they are not as in your face yellow as some others. More subtle when off, but intense yellow when on.
Not sure about Si but I can speak for the quality and fitment for fk8. It’s very nice quality, fits perfectly and sounds just right. Looks so good too. +1 to Josh, got me the best price of anyone. No regrets paying the little extra $ over the more popular options.
Added some cheap eBay vinyls today, carbon fiber vinyl stripe over OEM red. Door decals and the badge number decal on wing. Not sure how I’m liking the decals but loving the red stripe delete. Apologies for low quality phone pic. Looks cleaner after removing the transfer tape lol.