A couple guys at Escape Collective discuss the Carback on their podcast -- scroll a bit down the page for the link, then skip to 15:40 for that discussion. tl;dr: doesn't sound like it works any better than a Varia, but gives sellers a radar tail light with a larger profit margin than the Varia. (I can confirm that Garmin's margins between wholesale and retail pricing are razor thin -- only around 20%.) This suggests that bike shops might push the Trek unit even though it's not better than Varia. But if it's also not worse, that's probably okay.