I'll add two thoughts on the Champion. First- a while back there were issues with them processing orders in a timely fashion. I've not heard of this being an issue recently. In fact, a friend of mine just bought one from them and had it within a week.
Second- the Champion harness does not
clip into the seat belt buckle. They use a very heavy threaded chain link that hooks onto the belt. One of these:
You can see exactly how it hooks in here:
RATCHX3 High Jinks vom Neuanfang - Gotchya Day: 1/23/2013 DN, SG, SR, CA
Inspire Spark to Ignition! (Ignite) Gotchya Day: 10/8/2016
C-ATCH Pimg - RATO, UJJ (x2), DJX, HIT, CA, CGC, High in Games, Reserve High in Standard- CPE Nationals 2014