We looked at those a while back. It's a readily available wire crate with a hole cut in the divider that comes with that crate-available lots of places for a lot cheaper. The idea is a valid one though. It's sort of the same idea that we do with an expen and littler box.
It might work for your tiny babies, Tom, but I think that by the time they go to their owners, you might find that it didn't work too well.
When Kodi was a puppy, we took him on vacation in the trailer with us several times that first summer. We really didn't want an ex-pen filling up the floor space in the trailer, but didn't want accidents, either. So I thought I was "smart" and got a really BIG crate that would fit on one of the bunks in the trailer we had then. (the kids had already gotten too big for the bunks, so they didn't use them anyway) We put his cosy Pam-bed in one end, and a litter box in the other end. As you know, he was pretty reliably litter box trained by the time he left you, and this was several weeks later.
The ONLY times Kodi EVER peed in his crate was in this configuration. (and he did it several times) All I could figure was that litter box was too close to his "den", and he didn't feel comfortable using it. As a result, he kept trying to hold it, until he had an accident. He never ONCE peed in the litter box while it was in the crate.
We switched over to setting up the ex-pen in the trailer, in the 3x1 configuration, litter box on one end and his plastic travel crate on the other end and he never had another accident in the trailer. He just seemed to need more separation between his bed room and his bathroom!