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Richard,
I have a 12 inch Meade truss telescope. Don't know anything about the rigidity of the Skywatcher collapsibles but I believe that they have a Crayford focuser. My Meade Crayford focuser works fine.
There is no worry about the rigidity of the Meade. I can actually pick it up by the trusses and carry it, usually without too much effect on collimation. I would say both setups will require collimation checks after moving the scopes.
Loss of light is not a problem in an open tube design. However, a bright Moon or street lights can produce interfering glare in the lower tube. Anyhow, most of us avoid bright lights and do serious viewing at a dark site. I have never bothered with a shroud.
Whether the primary mirror is pyrex or BK7 glass probably isn't going to make a whole lot of difference. The main problem is the convection currents coming off the glass as it cools to the surrounding air. This gives images a hot or blurry effect. I use the fan to cool the mirror more quickly and it may also help to prevent dew on the primary. If you set up early in the evening with the Skywatcher, you will give the mirror time to cool down gradually for serious viewing. I find dew on the finderscope is a bigger problem.
The Skywatcher collapsible is quicker to assemble but the collapsed tubes will still be significantly longer than the bottom tube of the Meade, which can be carried as a separate item. Does it have to go in the boot of your car? I prefer to carry the scope with the tube vertical i.e. primary mirror horizontal (less jarring of mirror in frame). The collapsible will also be heavier to carry overall if weight is an issue.
Regards, Rob
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