"Bob - Child carriers are an absolute MUST for mom and dad to have! They have those you've linked and also slings/mei tai are options as well. They're great for any time you need free hands, happy babies, and hiking of course. As far as putting it into a bike trailer for security.. I can't recommend that as they can be unsturdy, bulky, and may not fit in properly."
I guess it could be "inferred" that I was including using a body-type child carrier in a carraige of some kind, but I wasn't and would not recommend that at all. never even occurred to me that that was a possibility in this case. ;-)
I carried my children in these kinds of "pouches" well past 4 y/o before I felt they were "on-their-feet" enough to sort of fend for themselves. We would get to our destination then let the roam while supervised so they could "discover" for themselves, and so we could be dumfounded as to how to answer their insightful and intriging questions! ;-)
Bob