The Devil's Business just came across as an extremely low budget made-for-TV movie. It was heavily dependent on the conversation between just 2 people for the majority of the movie duration. In order to carry that sort of setup off you're going to need some top quality acting and while the acting was occasionally decent in this movie, it was also sometimes below average.
Both Billy Clarke and Jonathan Hansler gave decent performances for the most part but Jack Gordon couldn't really match them for most of his on-screen time, although there was one scene where he demonstrated his true capability and that just about saved his credibility. Perhaps the scripting for his character was part of the problem. All the actors showed promise but they really needed more time and more takes to film the scenes perfectly. I assume either the budget didn't allow them to do this, or the director didn't spot the potential for improvement.
The writing overall was good and could even be considered the stand-out feature, it's just a shame that the budget couldn't be stretched considerably to make this into a real film and bring out the writing with cut-scenes and great cinematography. Instead, nearly all the action takes place in a darkly-lit small house somewhere in England. As a result, the visual imagery is just dull and boring for most of the movie and it gets tiresome rather quickly.
The production value was just a notch above the sort of movie a student might make at college or university, it was just so low that it was almost filmed like an episode of some British television show from the 80's, just sadly not with the same sort of entertainment value.
All the actors had some passion to their work, the writing was decent, the direction, while flawed, showed promise. But as a complete package, a fairly terrible movie that I just can't recommend. Maybe with a bigger budget it could have been a totally different story..