I have. Actually, they've been around for... well, not a
long time (AFAIK), but long enough to be one of the companies that makes the factory strings your new Rickenbacker wears. Along with D'Addario... Their flats are one of the handful of brands that I haven't tried in all the years I've been playing flats. But, now that I have my new Experimental Flat Wound Testing Device (
ie., a new bass I bought for this very task - and because it was kinda cool, of course), I will give them a try. Reports over on the Strings Forum are pretty positive about SIT strings...