hi Jonit,
I recently purchased a 12' GS premium dob which is exactly the same as the Bintel one.
What would you like to know about the 12' dob?
Focuser - As with previous post, the focuser is smooth to use.
Fan - The premium comes with a cooling fan attached. I live in north western Sydney and never had the need to use it so far. I may need it come winter time but thats a long way away yet......
The Sping tension - Sometimes I find it hard to put on and to take off, especially in the dark, some force is required, I have to use both my hands most of the time, but for a strong man it should be no problem.
The spring tension only works if the tube is not horizontal. Anything below horizontal level it will slide.
Mobility wise - To me the 12' is not very mobile, its definitely a 2 person job. I find the tube is too large to carry by one person, by that i don't mean the weight (to me its quite heavy though...) but the circumfrance and the slipperyness of the tube makes it difficult for one person to carry. \
I would not reccommend carrying alone even if you are well built, it could easily slip off and the mirrors and tube could get damage.
*I have attached two handles on the sides of the base and makes the base easier for carrying, however it is always better with 2 people.
Mirrors - Comes with pyrex parabolic mirror which means you will get some out of focus bits on the edges. But thats with all scopes that uses curve mirrors, some roughness at some point.
Focal Length - the focal length of the 12' is 1500mm. Which means that you will need an eye peice of at least 7mm fl to get 200x magnification. Something to keep in mind.
Eyepeices - I think Bintel supplies a 30mm, 15mm and 9mm with thier premium. I could be wrong. But these are all GS eyepieces, and to me (cus I wear eye glasses while viewing) the smaller fl eyepeices with small eye relief becomes quite a chore for me. So as with any telescope you purchase, a further investment is needed in eyepeices. but hey, maybe you don't mind the small eye relief that much.
Honestly, I have recently looked through a meade UW eyepeice, and a GS/Bintel wideview eyepeice, and they looked identical. I just could not tell the difference. One retails at 280 to 300 quids while the other I think about 70 to 90 or something like that.
So from this experience, I would have to say that GS eyepieces are quite alright in quality.......
I haven't looked through a televue though.... so I dunno what that is like..

but I heard it was the best eyepeices you can get your hands on.....
Anyway... I hope this helped. Feel free to post and ask more questions about GS/bintel 12' dob. I will answer them to the best of my nub ability.