Re: spare anchor
To the OP:
I think there are several good choices depending on your specific needs. For starters, since it's a stern anchor/backup anchor I would think that storage would be an issue. Do you have a stern roller or pulpit to hang it off? Will it permanently mounted, ready to deploy off the stern? Will you be getting it out of the lazarette locker and manhandling it into a dinghy to kedge out? All of these issues should help you narrow down the field of anchors that will work well for you.
My experience and disclaimers: I'm a big fan of the genuine Bruce and don't believe in cheap Lewmar copies. I've used the Fortress and Bruce extensively in the PNW as well. I also have a Mantus anchor (primary) that was given to me at a pro-deal discount that I plan to test shortly.
I would say the Bruce would work very well for you if you have a stern roller and will be stowing it there permanently. It's a great anchor for the PNW but it's awkward to move around and difficult to stow unless on a roller.
The Fortress is probably the best choice because it is the lightest, stows well on a pulpit or in a locker, and works well in the sand/mud that covers 95%+ of the PNW. It's also designed to only need 6' of chain which is usually a plus on the auxiliary anchors. The main failing of the fortress is that it might not reset if pulled from a different direction but this is very unlikely if used as a stern anchor.
Another good choice is the Manus. Assuming it is as good as the other next gen anchors Spade/Rocna/Manson it has the advantage over the other three of being able to be disassembled for storage.
My secondarym kedge and my stern anchors are Fortress anchors for the reasons stated above.
"True, your boat will outperform mine to windward, but my boat will always outperform yours at anchor." --MedSailor