The Circuit also has Thrax in their spawn pool, it’s just an alternative to running Zaramin Bounties.

Enemies also scale very fast in the Circuit (at least on Steel Path), which makes it easier to grind focus if you have a Focus Lens installed.

As Dystopia said Thrax are also present in Circuit, but there’s a few differences; Zariman Thrax become ghostly when their bodies are defeated and must be finished off with the Operator/Drifter. Circuit Thrax just die. However in my experience the Circuit, while reasonably consistent, is slower than Void Cascade because you’re banking on random spawns of Thrax verses guaranteed spawns from Exilizers.

I’ll also clarify that when I was doing this grind I didn’t do bounties. I generally did it solo using Styanax + Felarx. This is because longer runs, at least felt like they, were a better use of my time than several shorter runs. I think Exilizers start spawning faster in later rotations. The gameplay for Cascade gets pretty frantic going into rotation C while IME Cascade can be a more chilled experience on normal (or if you’ve got great options for the rotation even on SP) and PUGs seem much more willing to go the duration in Circuit than Cascade.

There doesn’t seem to be a rate difference for doing either in SP over standard so do whichever you enjoy more.