Yes, those are good racks for seed starting. (Temporarily) anchor it to a wall if you can - just in case!
I’ve used those outside to harden off flats before I had a greenhouse. If you move it outside, and use it with the cover, also anchor it somehow because if the wind catches it...Yikes!
Yeah, plastic connectors and no cross bracing. I imagine the cover is part structural. Was definitely planning on anchoring to the wall. Almost thought of getting two but if I were to get one for outdoors, I’d probably go with a bigger one. Sadly, none of the bigger ones are really made to fit 1020 trays, no matter what the brand. You get into the three digit price range pretty quick and they’re still cheapo stuff. Might as well build something in that case.