Do some Google searching - I tried to do some research on using a belt extender because the booster seat I have is difficult for my daughter to buckle on my F30 (sounds like a problem on the G20 too).
There are some varying opinions but it definitely wasn't a 100% safe to use a belt extender with a booster seat. In particular, this FAQ (
https://childsafetylink.ca/wp-conten...ster-seat1.pdf ) seems to be from a reputable source and said it is never safe to use a belt extender with a booster seat. Some people on the forum disagreed with the FAQ - but I'm not an expert and I'm going to guess neither are they. I'd certainly prefer to err on the side of caution when it comes to my children's safety, even if that means I have to crawl into the back seat to help my daughter buckle up.
Quote from the FAQ: "Can I use a seatbelt extender for a booster seat?
No, it is never safe to use a seatbelt extender with a booster seat. The extender changes the location of the buckle,
which then changes the starting point and angle of the shoulder belt, which could lead to an injury."