You'll find more traffic on BROL, so I recommend asking there as well. I haven't heard anything too negative about any of the Trident offerings (but I've never ridden one either). Used trikes are another option.
I also agree about 'bents and knees. They aren't any worse if you don't do silly things (i.e., use the seat back to really mash when you should be spinning).
Given somebody in your situation, I would recommend a recumbent trike, so I think you're on the right path.