design
If I was having Foss build me a rudder I would insist the design I had on my last boat, versus the small welding surface of the fingers they show on their site (left in the photo). The finger design is prone to failure at the welds, where the flat sheet design has a much longer welded area with just some reliefs cut out of the material to save weight.
By the way, I would also get a solid rather than tubular rudder stock.
Bob