"Mr Invincible" occurs after the events of "Miracle Day", but besides a few oblique references, there's no particular continuity of any importance here- this is a straightforward stand-alone Torchwood story. Jack is the key character here, with Gwen trapped.
Tom Price is an excellent narrator. On TV as the supporting character Andy Davidson he always seemed a little one-dimensional and weak, but as an actor he really puts his all into the reading and it works very well. He brings different voices to each character, without going over-the-top, and the story remains lively and energetic throughout. Unlike other reviewers, I actually liked Torchwood Fallout, where Andy Davidson is the hero. Here, he is reduced to a support character, but Tom Price is no worse for it either way.
Story-wise, it's got a couple of interesting ideas in it, but they're not necessarily in the right order. Mr Invincible himself is a little bit too much like a rip-off of the non-killable Captain Jack himself, and the idea of 'time pockets' sprouting up has been done in both Torchwood and Doctor Who before, so it's not especially original- but it is nicely paced, and has a couple of good twists. Captain Jack isn't really his usual distinctive self here- you could have almost any 'typical male lead hero character' in there and the story would still run the same. It would've made a good TV episode, but for the difficulties in filming eddies in the space time continuum ("is he?"), but it wouldn't be the best.
A decent but not classic story, very well told, and very enjoyable.