I purchased bt-021 front and rear for 2000 600s. I purchased them from Iron Pony in Columbus, Ohio, took rims in, they removed original battlax tires, mounted and balanced new bt-021, and disposed of originals for $290 (this included tax and disposal fee). Service was prompt and they didn't nick up my rims.
I remounted rims to bike and now have 800 miles on them. Before remounting I flushed fork oil, put in fresh 10 wgt filled to 5 1/2" down from top of fork tube with tube fully extended (this recommended in progressive spring instruction sheet), installed progessive springs from Dale Walker at Holeshot, cut pvc tube 1/2" longer than top of fork tube for preload(with bike on center stand for front suspension to be fully extended), and pushed fork tubes up in triple clamps on reassembly 10 mm (.396"). Ride was too soft, changed spacer to extend 1 1/8" past fork tube, this is very nice for freeway, decent 2 lane with twists, compromise on rough 2 lane (slightly rough, but not annoying). I am 44, good shape, weigh 185 with full gear, and am a seasoned rider. This info on progressives provided for those who need a preload starting point as I had a hard time finding tube length preferences here.
After getting scrubbed in and getting used to suspension changes I am starting to get more confidence in grip. They seem to be smooth and grip has not been an issue. Multi compound wear characterisics made me buy them as I commute straight line freeway in Cleveland daily for 250 per week, and run 1 day a week in 2 lane twists with a few long weekend 2 lane twist trips. Only 800 so far, but rear center doesn't even show signs of flat. I like them so far, but am comparing to 7 year olds tock tires at 7,000 miles. I do like the drop in for turns, but I am sure that is combination of lowering forks, springs, oil, and tires.
I will report in August on wear as I should have 4,000 on them by then. Hope this helps you out.
Bob