Hmm...
With such a potential scenario happening in, literally, the same seat and vehicle -
if the lock-offs on the seat are used, can I lock the belt retractor as well?
I've been thinking the answer to that is no - one or the other - and who wouldn't want to use the built-ins?
But, then I thought I remembered you locking the retractor AND using lock-offs in the Subie...
And, man, those Britax seats are just a joy to get in there. I went for outboard first, 'cause some pregnancy-effected portion of my brain thought that it had LATCH and that would be the easiest being this pregnant. Well, duh, it doesn't have LATCH, so next I went center. Well, I also failed to recall that Dodge blessed this vehicle with a non-locking lap belt. I DID remember that you could flip the buckle one turn to get it to hold tight, so I did...but then I couldn't get my hand next to the tall Britax shell to pull the belt at such an odd angle...10 minutes later I gave up and went outboard (which was the hardest with the roof curve and my non-conforming stomach. So, I get it in there, locked, tight, attach the tether and check the tightness one more time...and its loose. WTF? The super-long belt stalks were trying to mate with the LATCH bars. Out comes the belt, twist it, fall over backseat and tear a muscle, buckle and try to tighten the thing back down with that belly smooshed into the hard shell and my head against the roof...
It was much more dramatic and "colorful" in person, but you get the idea.