Yes, Off axis guiding can be a pain, as finding a suitable guide star at 1700mm can be tricky, however, the accuracy of guiding through a the imaging scope is much better than guiding with a separate tube when it comes to SCT's. As the primary mirror in an SCT is not fixed, it has an element of "flop" if it shifts/flops half way through a 10 minute exposure, your image is buggered. where as if you're guiding through an off axis guider, your guiding will adjust for the image shift, and all will be ok. Not to mention that guiding 1750mm focal length with a 400mm focal length (like the Orion ST80 Guide scope), whilst possible, is by no means "easy" and its all extra weight on the mount. a second scope, mounting gear etc... will easily take up another 2~3 kgs overall. (I know my guidescope/rings and dovetail is 3.3kgs... where as the off axis guiding setup weighs a total of 760g.. Better for everyone!
Cheers.
Alex.