I was looking into one of these bags. The vyna bond doesn't work well from what I've read. Seems like people like Marine Goop.

That is what we ended up using.  It worked out well.  The bag is awesome, my wife loves it.  I am thinking of adding one to my boat now.

Does it get in the way at all on enrty/exit?

No, it hasn't seemed to yet.  Haven't tried a wet exit with the bag, but I wouldn't expect problems.  It makes for a nice clean deck.  I think you could attach it even flusher to the top of the deck by not using the quickclips and modifying the way it attaches slightly, but it isn't neccesary for the high deck of the shearwater.

Just ordered an under deck bag for my Shearwater sport hybrid that I am building. I'm got it for the nice clean deck aspect. I don't want anything blocking the view of my soon to be cedar strip deck.

"Haven't tried a wet exit with the bag, but I wouldn't expect problems."

It would be a good thing to test though. If there is a problem I think it might be more of a problem when doing the re-etry, when you have to rotate your legs (and entire body) 180 degrees as you slide back down into the cockpit.