I recently stopped by Reeds in Walker and was able to compare them side by side.
Otter – Shorter not as tall
Otter – Slightly smaller square feet
Otter – No cargo nets inside for gloves jackets or other stuff
Otter – Smaller Skirt
Otter – Darker in side
Otter – Removable windows
Otter – Great Name brand
Clam – Considerable taller than the otter
Clam – Slightly more square feet
Clam – Two cargo nets on the sealing
Clam – Larger skirt
Clam – More light coming through the fabric
Clam – Windows not removable
Over all I was not that impressed with the Otter compared to the Clam. You have to duck further down to get in the door and once in it felt much smaller which I accredit to more the shorter hight vs the square feet difference. And then with no Cargo nets and shorter skirt for banking up……. Looks like a Clam might be in my future!