Regent install with LATCH & seatbelt & tether?

[emmasmama]

45 lb child, Honda Odyssey. I told my DH we had to switch to belt install and he rolled his eyes at me because of course, it says in bold ON THE CARSEAT that you don't do this until 48 lbs, but I told him for Honda's the LATCH is only rated to 40. Anyway, he installed it with the latch + seatbelt + tether. Can someone tell me why this wouldn't be okay? It seems to make sense because then you're triple covered, but please school me if I'm wrong.

[Joolsplus2]

It's one of those misuses where it MAY have failed (by the straps being so tight that the energy is transfered into the child versus absorbed by the straps...G-forces in the chest are 'too high' and may result in injury), or it may be nothing wrong with it (I don't think crash data is forthcoming that kids with both systems are dying like flies...), but is it necessary? no. recommended? no. But I won't tell you it's a horribly dangerous misuse, just that I would not personally do it :)
Julie CPS Tech and mom to 3 in seats
http://www.cpsafety.com/articles/RFAlbum/SarahMA.aspx