@Andy - I don't know about PDW being a "big company" [guess it's relative], but definitely looks like an identical concept. Now a tiny niche market is divided... Bummer... Sounds like legal issues could be looming.
On the tangent thought of seat bags... What I'd like to see - any bag makers out there listening? - is a seat bag which attaches to the top of the seat stays and better utilizes the space closer to the seatpost and lower on the bike. Not really much volume space to take advantage of on a FS bike, but most hardtails have quite a bit of unused room above the rear wheel.
Edit addition - both designs need to ditch trying to make the twos rods coming together at the seatpost clamp totally rigid. Aluminum rods with holes = stress failure at seat collar. Aluminum ring around carbon seatposts also a bad idea [which is noted by PR]. The seatcollar joint needs to a heim joint or something a bit softer to allow some degree of freedom. Just the triangulation of the two stays coming together at the seatpost is going to really cut down on swaying. Two carbon stays at the bottom of the tray, forming a triangle with an apex at the seatpost joint [plastic/fabric/webbing heim equivalent]... or even attaching at the top of the seat stays... and you have another similar manifestation of the design concept.
If you are looking for a bag manufacture who utilizes the space from seat stays to saddle check out Rogue Panda Bags. Their Picket Post bag does just that.
http://www.roguepanda.com/shop/picketpost-seatbag/