We've been using that when we want to bring our chicks outside (they're still too young to be outside full time). The smallest ones can squeeze through the gaps but they won't be able to for much longer. It's not something I would leave alone for even a second though since any dog or anything else could easily knock it over.
Portable chicken runs are called chicken tractors, and if you do a search here you'll find lots of ideas and pictures. Something like that temporary pen in the link isn't going to keep your chicks safe from any daytime predator like a cat, dog or hawk.
Yes, quite well aware of the tractor concept. I live in a urban setting with a back yard that is about 75x75. Not a lot of room to add a structure like a tractor too, plan on having a permanent run but just looking for something portable and easy to store to put them out to play in the grass. This would be done while we are out working in the gardens etc...
The full yard is fenced with a 4 foot picket type fence. Just may let them wander while we are out.