This is a cute product. Kind of a non-necessity but something definitely worth looking into if you're like me and insist on a completely airtight capsule so absolutely no diaper matter stench seeps into my breathing space.
Diaper Baggies are just that - bags for diapers.
Definitely useful. Not cheap though not cost-prohibitive. They're diaper disposal bags with a zipper close feature. Nice when stuffing a nasty diaper into it. Kinda makes the whole stink factor a wash.
I did a brief stint as a flight attendant many years back and I CANNOT tell you how many parents tried to hand me an unwrapped, stinky, germy diaper when I was handing them their 'meal' of peanuts and drinks. Now, there are two sides to this as for some reason for which I cannot for the life of me identify, some planes STILL do not have changing tables in the miniature restcubes uh..rooms. Weird.
Anyway, Yes, a Ziploc bag would do the trick but I did notice three distinct differences over the Ziplocs.

One is the Ziplocs are thicker and take up more room in the diaper bag. Secondly, Diaper Baggies are made from recycled plastic which I dig.And, lastly, Diaper Baggies aren't made of clear plastic so no innocent party has to see what is actually lurking in the bag.