My family and I got into Pops pretty heavy back around 2016-2017. $8 a pop (pun intended), they made really inexpensive little gifts. Did good on a spelling test? Surprise, have a Pop! I was thinking about you today and grabbed a character you like, have a Pop! That kind of thing. They were fun for a short time, we ended up with all of the DCEU pops from BvS through Birds of Prey, as well as a ton of comic DC stuff and some random movie ones.
I've never really considered whether they "go with" anything. I mean, I wouldn't put them on the same shelf as a diorama with specifically posed figures, but I do have some Superman pops on my "Superman Shelf" of random Superman things (figures, pops, statues, pins, cups, etc). They go just fine wherever you put them, as long as you aren't pretending they're an action figure.
I'm not surprised or sad to see them go. We stopped buying them after that initial couple years, but they are truly everywhere. It was weird walking into GameStop or Hot Topic and seeing that half of their store was dedicated to Pops...the bottom was always going to fall out eventually. As for Mondo, I have their Mumm-Ra and She-Ra 2.0 on preorder. I've never purchased anything else from them. My plan was to get Lion-O to go with Mumm-Ra and grab a He-Man to go with She-Ra and that was all I wanted/needed. Looks like I'll be fortunate there, if Mondo ends up affected.