The multiple-personality angle doesn't work. The quality is a little low and the writing isn't there to really sell that aspect... but... Stephen Medvidick does a great job with what he has to work with. He sells his role as best as he can with what he has to work with.
It's understood walking in that this is a low budget production, the quality isn't going to be there. You have to watch it understanding from the start that it will be an uneven film.
And it is... some of the script needed polishing and some of the actors were horrible. And by "the script needed polishing" I mean that is wasn't a bad script, it just wasn't fit to print.
However, Stephen Medvidick was not, he sold his role, and so did a surprising number of other actors... unfortunately not many others in leading roles. The killer and most of the victims and potential victims did a shockingly good job for a low rent movie.
The lighting and cinematography were also there. They understood how to hide the budget in the lighting and they understood how to bring faces out of a dark environment. And they understood how to use both to create tension to create tension and atmosphere.
Over all, it feels like a film with mostly pro-talent working with a D grade budget. It's not bad.