I think TS means stepping in and kneeing the inside thigh of an incoming roundhouse instead of checking it. Malaipet showed this in his DVD somewhere I think. you better have great accuracy with your knees or you'll be eating roundhouses to the body/support leg if you miss.
as far as checking with the kneecap, some people advocate it but I don't do it. my shinbone right below the kneecap is built up a bit now from checking so I just use that (like a normal person lol).
valid but tough to pull off...smaller margin for error than a shin check.