I'd stay away from the one-part. My experience with it was in the tropics and it just doesn't hold up to the sun. Not familiar with the ALEXSEAL products but I've had a lot of experience with Awlgrip, Sterling and Imron in commercial settings. According to the link above the ALEXSEAL product seems to be quite similar.
s/v casa chica
S&S Swan 43
Keep the boat IN the water,
keep the water OUT of the boat.