|This article mentions that there's no evidence that this chair was ever put into practice but it sure looks mean. As far as interrogation goes, I don't think many prisoners would hesitate to talk upon seeing this monstrosity.|
Honestly, it looks a bit too over the top for my tastes. The razor-sharp blades would be effective in intimidating someone but that center blade on the back is more likely to slice the spine and possibly paralyze your would-be confessee. Subtlety is required here. I would opt for the retractable blades. Strap the victim to the chair and then bring out the blades.
Of course, this is just one of many such devices of torture. A variation on this one may make an appearance in the story I'm doing research for. As you may imagine, it's not a happy tale.