Jenny was created during the Tennant episode The Doctor's Daughter in the most obvious set-up for a spin-off that show has had since its revival. That never actually came to anything, presumably because most of the spin-offs had very short lives, and they predicted similar for this one.
However, Big Finish have been filling that niche for a very long time, expanding the main universe, particularly with the companions, and they've had a crack at Jenny.
Georgia Tennant reprises her role as the titular Jenny, and is joined by Sean Biggerstaff as Noah, her own companion. Jenny is luckily more or less fully formed as a character (I suspect anyone who hunts down this has seen the relevant episode), so there's not much to be done by way of introducing her and her approach to the world. Noah, on the other hand, has a mysterious past and not mcuh knowledge about the universe, acting as both a handy plot device and a useful audience surrogate.
Chasing them is the COLT-5000, a killer cyborg which intends to use them for its own nefarious ends. The COLT is voiced by Siân Phillips, which makes for an entertaining villain, both friendly and wildly threatening.
It's the usual approx. hour long episode format, with standalone plots but with the single chain of the chasing COLT running through them. We've got troublesome scavengers as an introduction to the series in Stolen Goods, a "struggle in suburbia" episode in Prisoner of the Ood, a social commentary episode in Neon Reign and a bit of philosophy and violent climax in Zero Space.
It's Big Finish, so you know it's both well produced and well acted. The foley is spot on, and the dialogue is always snappy. Jenny in particular is very snarky, taking a cue from Tennant's style, with a little more violence thrown in. I did find that to be a slight problem, with the repeated callbacks to Tennant's run on the series feeling a bit like an anchor around its neck.
It also feels a bit too much like a standard Doctor Who series. That sounds odd to type, but I was expecting something rather more different. This could have been a stock episode. Something that pushed it further from the original series might make me more likely to hang around for a second release.
Still, it's the usual excitement and thrills with an excellent cast, so it's worth having a look at if you were a fan of the spin-off idea. It also has an excellent theme, riffing on the original with a military bombast thrown in.