I bought a CEM120EC2 21 months ago to see if it matched up to the AP1100 and the SB MX+ which, all in, run an extra 3 to 4K dollars in the USA without encoders, with slightly less rated capacity and not as much through the mount cabling. (Overseas, I suspect that the difference in price would be even greater.) I had the luxury of a permanent pier at the time and I realized that my old AZ/EQ6 was not a good choice for remote imaging. The older I get, the less interested I am in driving 100 miles in two directions to image. So, that was really the idea- set it up on the pier and log in from home and see if the price was really right. I had my MX+ to fall back on if it didn't work out. Over the 21 months, it's been an interesting road, but I really think that the mount does in fact compare well to other more expensive mounts with the same capacity for most use cases.
My software suite for the mount consists of MaximDL and CCD AutoPilot. These are well proven solutions for fully automated remote imaging and have no bugs that bother me at this point. On the Paramount, I use the SKYX instead to get the benefit of Protrack. I'd use the SKYX on the CEM but the telescope focusing software from Planewave only supports MaximDL. I find it to be the best focusing software out there. Both systems are run using small cheap Win10Pro computers with modest i5 chips and 4GB of memory with SSD's.
The first night that I had the mount, I had to set it up on my pier and connect everything to it. I then found out that I had to download and install all new software to get it working on my Windows computer. Overall, I wasn't really ready to do anything with it until around 4 hours later. I then polar aligned the mount, focused the telescope (5" refractor) and calibrated the guider. By 1AM I was able to guide very very well. At that point I went home quite happy. I was really happy with the fact that all of my cabling was through the mount. The mount has 4 USB 2 ports and 1 USB 3 Port. The mount squeaked a bit when slewing which was worrisome but that didn't seem to have any effect beyond making me nervous.
The next clear night I ran into all sorts of problems. First, the pointing model no longer worked. The scope was over 1 degree away from any target. I had to build a new pointing model. That continued for about 5 months until iOptron fixed the driver. Second, the mount would not park at it's zero point - looking at Polaris. This was also a driver problem. When I tried to park, I came within an inch of a pier collision before I could stop it! I then parked elsewhere for a while. They fixed this at some point in the driver software, probably about 6 months after I got the mount. Once I got by this, my first slew was off by 1 degree every time. I finally came up with a workflow of re-establishing the zero point each night and then parking the scope. (Note that there is a built in GPS so the mount knows precisely where it is and what time it is.)
Overall, the software that comes with the mount is simply poorly designed and has stayed that way for two years. Everything essential works, but it's obvious that no one at iOptron understands the basics of GUI design. First of all, you need to have two panels up - one just connects the mount and another has most but not all of the mount parameters. Another panel has (yup) some other parameters that might interest you. Yet the entirety of all this could easily be in one panel for ease of use. On top of that there are quite a few "settings" that still, after almost 2 years do nothing. There is, for example, no pointing model software (but you can store some calibration results). If you have a problem you can't turn on/off the encoders or the guiding in DEC (but you can in RA).
Leaving the software aside, the mount is also missing a couple of features that I would really like to have. You cannot use it to track comets or asteroids because you cannot dynamically vary the DEC and RA tracking rates the way that you can with an AP or Paramount. I have no idea why this is the case. Any mount aspiring to be used in an observatory should be able to do this relatively simple task. The mount simply will not run well enough to take long exposure unguided images. Period. I can go maybe 2 minutes and that's that.
Support has been spotty. I had a problem with the system one night - oblong stars - the first time I put my PW 12.5 on the mount. I figured it was a mount problem and I wanted iOptron to take the mount back and fix it. It took me at least 3 weeks to get an RMA. By the time I got it they had released a new driver which they said cured the problem. It didn't. Eventually, (my bad) I worked out that the fan in my camera was vibrating. The camera is now fixed and the stars are perfect. What I have found is that the best way to deal with iOptron is via email, calling them is pointless and the forum is poorly monitored. I've gotten responses late at night but it's pretty clear that any tough question needs to be answered back in China.
One other thing. My mount can be provoked into unstable behavior in the DEC axis. Any guiding cadence below about .5 seconds will cause the mount to oscillate for about 2 minutes about 2 arc seconds in DEC. RA remains perfectly stable. I have no idea why this happens and since I guide at between 2 and 7 seconds, I only noticed it when someone asked me to run a test. SDE has also been mooted and may be there, but if it is, it does not seem to affect the performance of the mount. I have about 70 pounds of weight on it and I image at 2.5 meters of focal length these days. The one other CEM120EC2 that I've worked on works just as well. As always, I'm sure that there's a bad one lurking out there.
I'd love to hear from other owners about their experiences. I also thought it was time for a report now that the mount is almost 2 years old and is still going strong.
At this point, I have a stable, easy to use, environment - my driver is 6 months old and the mount is on a permanent pier in an observatory. I've even been running it remotely from home for the past month from home and it works just as well as the MX+ sitting about 10 feet away from it. I would recommend it to anyone who's price sensitive and doesn't mind a slightly awkward workflow, will accept average support and has pretty standard pretty picture aspirations. With the Paramount, I just turn it on, home it and it's ready to go. With the iOptron, I have this little routine that I have to do which takes about 5 minutes each night. There has been little or no performance difference between the two mounts.