I visited Shawn's showroom last January and loved every minute. We met at 9am on a Saturday and I must've sat there and sampled ukes and talked story for 3hrs! Aside from having an amazing inventory of ukes for sale, he has a handful in his collection that are not for sale, and few that belong (and have been in museums). That visit might be the closest thing to going to an 'ukulele museum you can get on the entire planet and the docent is the owner, 'ukulele lover, and fellow UAS sufferer... maybe one of the worst!
He's a fount of 'ukulele knowledge... both historical, current, builders, and musicians.
It really depends on what you're trying to get of your visits. I haven't visited the Kamaka or Kanilea factories, but I did do the KoAloha tour. It was fun to see how ukes are built and chat with Paul and Brian a little at the end.
Going to retail stores, you'll see some cool ukes from each retailer.
Shawn gives you a boutique showroom experience where you can A/B some of the best ukes from some of the best builders. You can hear and feel the differences between an I'iwi, Kinnard, Moore Bettah, Grimes, G-String, etc etc... whatever amazing stuff he has in stock.
I can honestly say there's nothing else like it.