The idea sure was great, but IMHO it also took much of the beauty from rowing. The real point in good technique (and we know how difficult it is!) is in having a smooth recover and quick catch, gently "riding" the boat and controlling the negative forces that make the stern pitch. Ironically Kolbe, who popularized sliding riggers through his 1981 victory, was an absolute master in this respect, so (again, IMHO) he was the one who needed sliding riggers less.
I just recorded an interview with Volker Nolte who was part of the team who developed the sliding rigger in Germany. Full interview ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-9r--wbkUx7w.html
Imagine what athletes today could do with these. Good thing they banned them... 7:00 flat back in the day. Hell, breaking they would be cracking 6:00 with them now, guys can get way down in the 6's without them.
