ATC is simple*, small and lightweight, but offers no other advantages for canyoneering, in general. Especially none that outweigh its significant disadvantages, which as you say have been DTD. That said, it does have devotees and a niche or two, esp. among GRCA canyoneers (aka gram-a-neers). Nanogrammers? And Mae West-ers.
Anyway…
Prior discussion:
http://canyoncollective.com/threads…hat-do-you-like-about-each.24679/#post-105482
p.s. are you aware that the guy who inspired this thread was using an ATC?