It's a reasonable upgrade to their appearance, given both improved CGI and a more mature rating. Makes it feel like they're still living beings, even in goo form.
The bucket was a little weird. A changeling could rest in pretty much any enclosed container, such as the various drawers Seven was rummaging through, or could just replicate a bucket as needed and then return it to the mass buffer afterwards.
Yeah, them showing a "changeling" bucket and then having that be exactly what Seven finds was a bit of plot contrivance. But it moved quickly and didn't detract from the episode, IMO.