Barry the Nomad on Sonic Retro posted this recently.
I remember that promotion because it was the first time I remember ever being affected by TV advertising. I wasn't even really a Sonic fan yet (we never had a Sega Genesis in the house)--but my aunt had a toy at her house that was built the same way as the flying Tails toy, and I knew that sort of thing was fun and wanted one. And Sonic was cool. Every kid my age either knew that, or consciously denied it, and the latter only if they were especially loyal to Mario.
I never actually asked my parents to take me to McDonalds, because I already knew they disapproved of the place, and that they would only think less of me for asking.
The Robotnik toy is especially amusing to me now when I consider that so many "building robots for beginners" projects are to build a robot that avoids obstacles and table edges. It's not surprising that the cheap '90s plastic toy doesn't do so well at it...but the mechanism required is still simple enough that it makes sense they'd at least have the basic idea down. It's all that decoration that hangs over the side and throws off the balance!
I also remember that train promotion in the last part of the video, though I don't remember ever getting a good close look at any of the toys (a natural consequence of not actually going in a McDonalds). The TV with the Genesis on top is a pretty cool idea.
I had some friends who picked up one or two of these toys each, but in general, they were just outside the periphery of my Sonic experience. Just as well; the plushies and Dreamcast I ended up with take up enough space as it is.