Guðbergur was an excellent host and very communicative upon arrival. We stayed in late February and had some historic weather (>30km/hr winds and >50cm snow overnight). That made for a little rockier time, but gave us all the more pride in being able to call ourselves "sailors". Otherwise, the majority of the time, the water is really calm.
There were 3 in our party, which gave us a lot of room to spread out. The boat itself can sleep 10, with 1 bedroom in the front, 2 on either side in the back, and 2 sets of narrow bunk beds. Put the heaviest sleeper in the back on the dockside, since the heater and the dock make noise at night.
There were 2 bathrooms with toilets and 1 with a shower. After 700L, the water will need to be refilled, but we didn't run out over 4 nights. Fully explore the kitchen area, we missed the second drain and icebox for the first night or two. Guðbergur provided plenty of linens, shampoo, and the blankets kept you super warm.
I'd recommend googling the directions and printing out a map prior to arrival. It was difficult for us to find with the dark and snow, because we didn't immediately see the boat, but I promise it's there. Also, check out the tide times; it's 10x easier to go up and down the ramp with luggage at high tide, and that only really happened to us once. Try to pack light-ish if you can, since you have to load everything on the boat.
The location is pretty perfect for getting to everything, and you can use Icelandair Hotel Reykjavik Marina as the pickup location for most tours (its right in front of the coffee shop). There was easy parking for the 2 nights when we had a rental car, but unfortunately, the Hertz at the marina was closed.
A great experience as long as you are prepared for a camping lifestyle. Highly recommend and thankful that Guðbergur shared his awesome boat with us!