I'm seeing a ton of dawn redwoods showing up in nurseries. They've got them pretty much everywhere here in NC, and they even have big ones in landscape at my local Costco (which was opened about a year ago).
Though dawn redwood is a little smaller and easier to work with than coast redwood, everything is relative. They still grow naturally straight as a pole, with very little taper. It is difficult to get nice caliper at the roots and also get a gradual taper to the apex. For bonsai, most people prune the top off, leaving a jin, and wire up the next highest branch as a new apex. It is a reasonable solution, but after you see many trees styled this way, they tend to get a little boring and repetitive. Bald cypress is similar - and has similar challenges.
That said, if you want to buy it because you like the species, go for it! Make sure you prioritize nebari - the surface roots where they meet the soil and trunk flare at the soil line. In your nursery tree example, you can't see the roots, so you need to dig down to see what you're dealing with. If the roots are all on one side, or if they are only a few overlarge roots, I would skip the tree and look elsewhere. You are looking for symmetrical small roots that flare out from the base like a pie... and many nursery trees tend to grow roots downwards instead of radially.