Looks like you're paying $60 extra for the tube rings on the OTA version and getting the dob mount for free on the other.
One difference to be aware of is the 'OTA only' is a F5 and both the others are F6. The F6 is a longer tube than the F5 and will provide 20% more magnification when used with the same eyepiece. On the other hand, the F5 will give you wider views with the same eyepiece over the F6. You prolly know this...
not sure about the tension handles, someone here will know though..
Check out Andrews -
http://www.andrewscom.com.au - they have the Skywatcher OTA for $399 but they also sell the GSO.