A GEM needs to be polar aligned. That is unnecessary with a alt-az mount. GEMs are inherently more complicated than an alt-az mount, they require counterweights so they are heavier and require more robust construction. They also require a third adjustment to provide polar alignment. GEMs are particularly problematic with Newtonians, large Newtonians in particular. The rotation of the OTA, focuser and finder as one moves across the sky, fighting with the counterweights, it's not all that easy even with rotating rings.
Jon, I have three GEMs. When it comes to my polar alignment routines, all I need do is take out one of those tripod/mounts, set the tripod feet on the ground, utilizing a bit of "Zen"
, and the mount is instantly polar aligned -- no second nor third adjustments required.
One of my GEMs is 30 years old. I've not so much as "tweaked" it's latitude adjustment, nor its azimuth adjustment since that first time I set it up 30 years ago. The GEM shown with "Little Red Riding Scope" (see my previous post) is 24 years old. The adjustments on that mount haven't needed to be tweaked in the past 24 years. Then there's my most recent GEM, acquired in 2015. As with the others, it's needed no further adjustments subsequent to the first time I set it up.
That's the way it's been for me and my GEMs -- for my strictly visual purposes, with my strictly manual usage, with three of my refracting telescopes.
You want to talk about weight? Just how do you think the weight of the GEM-mounted scope that I posted a picture of (an 80mm f/5 achromat) -- with its counterweight, mount and tripod -- contrast with the weights of either of the Newtonian reflectors (even without their mounts) in the photo that you posted?
You're right, large Newtonians do have a lot of potential problem areas that their users/owners have to be aware of and have to address. But clearly in this thread, in my previous posting, I wasn't referring to large Newtonians.
For me, with my observing style, with my equipment, I get the benefits of a GEM (easy tracking via movement along just one axis) without all the hassles that would apply to Newtonians, go-to mounts, and/or imaging setups.
There are more than one way in which a GEM may be used, just as there are more than one kind of telescope that a GEM can be used with. A GEM can be a pain for some to set up and use, but that doesn't translate into those mounts being pains for everyone else to set up and use.
Let's relax and enjoy the Zen of our astronomical passions
.