A fresh searun will have the same deep red meat as a salmon. Excellent rich taste!
On the Necanicum, they won't be running until early September or the first rains (I spent last August learning that). During the summer, I've heard you can find them in the bay below the 12th St bridge, but I've not spent the time to personally confirm that (hopefully will make the time this year). A few fat searuns will poke into the lower river above tidewater in late August, but you'll fish 2 miles of river to find one big fish and it usually takes a little rain shower before that will happen.
As the season progressed last year, I saw far more coho & chinook than searun cutthroat, but caught way more cutthroat. In fact, I only landed one coho jack (released) and one small unclipped steelhead (released) and hooked one chinook (it threw the hook as I was banking it). IMHO, the cutthroat are far more aggressive in attacking lures than salmon or steelhead.
Keep or release? At a limit of 2 fish per day, why waste it on 8"-10" fish that will probably go to sea soon? Use the bag limit for the big ones.