I saw them a few times in zoos, or other exhibitions with terrariums.
I love keeping insects and other invertebrates, and first I had looked into getting a train millipede (saw them while living in the US, but never got one as we were constantly moving between states and it always looked like we might move internationally soon which we finally did). Then here in Chile, I looked again into getting a train millipede - not available. (I don't know if not allowed, or simply not available.)
Once when I ordered dubias, there was an offer to get hissing cockroaches for just a few bucks extra. I ordered them and kept the big ones (were half of the size shown here when bought) as pets, and fed the small ones (size like feeder dubias) to my dragon. The next time I again ordered the "dubia and hissing cockroach combo" and again kept the larger ones, fed the small ones to my dragon.
(Some say they are aggressive and a choking hazard. Never observed for tiny/ small ones: they are like dubias. What I fed was even just at the size of isopods. I have seen online there were some claims that a bearded dragon died after having fed a hissing cockroach; here I strongly suspect a much too large one was given. Overestimated, or some people even find it funny to offer giant prey. For sure I will not do that.)
One big, big caution when keeping hissing cockroaches: They climb glass and other smooth surfaces very well and they are very strong. So, they open lids. A typical terrarium or aquarium lid won't hold them in. A lid like from a tote or tupperware container also not. We tried a few "but this will hold for sure!", and then had escapers. Remember one as fat as in the picture hiding behind a dresser - my husband removed the dresser, I grabbed the roach. Number 2 was stomped dead in front of the elevator, so escaped the apartment.
Number 3 was found 2 months after when my husband, wanting to grab something from the bedroom after dinner, saw some "dry leaf" on the floor in front of the bed, and then he recognized, no dry leaf as it run off - was a hissing cockroach. After it run off, he took half the bedroom apart (mattresses out, emptied closet...) to find it. He was successful.
I finally got a large airtight "lock and lock" food box for them as a terrarium (drilled fine holes in the lid). That's impossible for them to open.
The hissing cockroach on this image is actually a bit larger, means, here it has "compressed" itself a bit. When it's in the bin, you could add approx. 25 % to that size.