I've only had a few nights with the new mount and I probably should wait till I can give a more authoritative review. . .but for what it's worth, here's my perspective.
The CEM25EC was my first mount. I've had it for two years and until a few months ago I didn't guide it at all; just went with the tracking. Which was pretty good: I generally ran 2-4 minute subs with my 4-inch refractor and the stars looked pretty round. Keep in mind I'm new, though. I really liked how quiet the mount was (is); I found it pretty easy to work with. And my lower back really liked how small and light it is. I'd still recommend it to anyone except that, wow, this new CEM40EC just blows it away! Only a little heavier but far more professional in it's fit and finish. Where the little one had plastic knobs and mushy belt drives, this one feels solid and secure. I had mixed success with the SharpCap polar alignment (possibly due to operator error) but the iPolar alignment is much easier and seems to do a great job. The hand controller is bigger with more options and better features. The mount has a couple of USB connections and you don't even need a hand controller (though after a couple of collisions with my CEM25EC I always keep the controller and the Stop switch in hand during a big move). The cable management system isn't what I'd hoped but it's a step in the right direction. The mount holds and moves my TeleVue np101is and Skywatcher SkyMax180 very well and I'm confident I could use a much heavier scope. (The CEM25EC didn't seem to have any problems with those, either.) I've only had a couple of semi-clear nights but the tracking looks good. I have tried unguided but PHD2 doesn't seem to be working very hard, so that's a good sign.
With the old CEM25EC the mount would ram into those little azimuth pins on the side, hence my cheesy rubber bands to keep them out of the way. Overall the mount worked great, but there were little things like that that gave it a cheap feel. The new CEM40EC has none of that--and it doesn't ram into itself.
It came with the new LiteRoc 1.75inch tripod instead of the 2-inch I'd bought with the CEM25EC. The extensions are the same diameter as the old 2-inch and it seems every bit as stable.
Hope this helps somebody. I put off buying the new one because hey, the old one worked pretty well. But technology advances and the new mount shows it.
Edited by FrankSD, 05 August 2020 - 12:17 AM.