What I wonder about this idea - it sounds like they started out with a open house for everyone who applied, regardless of qualifications, instead of phone screens. So how many really qualified candidates are going to be interested in travelling out to the company for an "open house" with everyone else who applied for the job?
From a candidate's perspective, the phone screen lets you prove yourself to the company and get to know them a little before taking the commitment of actually going there - usually during business hours, possibly disrupting any job you're currently working at. I feel more comfortable taking time off to go there when they've already proven that they're serious about me and I know that they've evaluated me well enough to know that there's at least a good chance I'm a fit for the position.
From a candidate's perspective, the phone screen lets you prove yourself to the company and get to know them a little before taking the commitment of actually going there - usually during business hours, possibly disrupting any job you're currently working at. I feel more comfortable taking time off to go there when they've already proven that they're serious about me and I know that they've evaluated me well enough to know that there's at least a good chance I'm a fit for the position.