i used to have the burton SIs and i liked them. i used to ride solo (or with skier friends) a lot so i could take a ton of runs without having to stop at the top. i never had and performance or reliability issues. then i started riding with friends so i was sitting at the top waiting anyway so i went back to straps.
like KC said, people stopped riding them. and companys stopped taking their pro riders advice on them so the R&D went down the tubes.
if you still really want to ride them look on ebay, they are still floating around there. in fact i still have step-ins and boots floating around a closet somewhere.
Passion Over Fashion