Describing the bike seat to you is great & everything, but really you should just watch the video to get an idea of what it looks like & how it works.
Glen & his wife are mountain bikers, so he designed this seat with trail riding in mind. The child isn't seatbelted in, so s/he can stand up to go over bumps, just like you would on your bike. They aren't likely to fall off because their feet are strapped into the foot pegs & there is no need for an extra set of handlebars--they can just hang onto yours. Because the seat is just a narrow plastic saddle, the adult rider doesn't need to bow their legs out around it. You can also use your knees to support your child a little when not pedalling & they're positioned between your arms. Though you might worry about them not being belted in, it feels very secure as you're riding. I imagine that because the upright position feels similar to riding a bike, it might help them when they learn to ride their own bikes too.
The Mac Ride isn't in production just yet--Glen is still working on getting funding. I'll let you know as soon as their crowdfunding campaign kicks off so you can be a part of getting this great seat to market too! If you want to hear more about the Mac Ride, keep up with the crowdfunding & news about the project, follow them on Twitter, Facebook, Google+ or sign up for the mailing list here.
Follow Spokesmama here too: