Personally, I think the creation of a codex that is designed specifically to be used as allies is a great idea, and hopefully this is not the last such codex that we see.
From the latest Black Library update:
Few individuals embody the grim darkness of the far future like the dreaded Inquisitors, mysterious and clandestine individuals who hold incredible power and influence. This new codex is packed full of background and stunning artwork on the forces of the Inquisition, from the Ordos that make it up, to Inquisitors of legend throughout the Imperium (including some old favourites who might be familiar to fans of Black Library books…)The rules in this book allow you to add the agents of the Inquisition into any Imperial force (as well as fielding them, begrudgingly, alongside the armies some of the less belligerent alien races), or field them as an army in their own right.The main focus is very definitely on the individual Inquisitors themselves, with every Inquisitor now having access to a bewildering array of options, wargear and armour, making them one of the most customisable characters in the galaxy (as it should be).There are also plenty of ways to represent your Inquisitor’s alignment to a particular Ordo, from weapons, unique Inquisitorial relics and three Warlord Traits tables for Xenos, Hereticus and Malleus Inquisitors.Speaking of Warlords, this codex allows you to have an Inquisitor leading your Imperial forces, even when he isn’t part of your Primary Detachment (would you argue with an Inquisitor about who’s in charge?).Of course, Inquisitors rarely travel alone. Instead they bring with them experienced warriors and specialists, not to mention their pick of the best transports from across the Imperium.This is great way to represent your Inquisitor’s own particular field of expertise. Will you have a radical Inquisitor leading ethereal squadrons of Daemonhosts, or an experienced alien hunter with a pack of Jokaero Weaponsmiths in tow? Of course, you’re welcome to mix the two if you like (but we can’t promise that your space-ape and possessed monstrosity will play well together).