DD has this toy and loved it on her infant seat. We moved to the convertible seat this week and I figured out that I could attach it to the tether straps on the convertible. Yes, I know the tether straps are not there for toys, but if it keeps her happy in her car seat, I'm less likely to be a distracted driver.
Re: toys for convertible car seat
The tether straps on our Britax go from behind the car seat and fasten to the back of the seat on the car.
***Not my kid. Got the pic off a car seat website***
We were told that if we didn't have tether anchor points on the floor we could NOT tether our Britax rearfacing?
Also I'm glad you found something that works but I wouldn't risk it, IMO. You aren't supposed to add things like that to the carseat at all. If there was an accident the toy could seriously injure your child.
My car seat manual and car manual both say to anchor the tethor straps the way I have them.