Frankly I can be very short on this piece of equipment: indispensable.
Let me explain why. Unless you use an upper-class mount like 10-Micron or otherwise (expensive) pieces of metal, guiding is absolutely essential to get perfect images. I tried to use PHD first, but it just didn’t work out for me. Too much things to fiddle around with. In some cases it worked beautiful, in other cases the PC was sounding the alarm constantly to get me crazy ‘lost star’ or whatever. Sometimes it seemed to work fine but then the images were trash afterwards. I’m sure there are lots of people out there that do have the skills or patience to get PHD working, as many pictures evidence.
I have a demanding full-time job. I need my sleep. So ….. indeed what I want to do is setup the telescope, align the mount, frame the object, verify a test-shot …. and then leave everything to image automatically ( taking a risk). I do that using a DSLR and the Lacerta autoguider. Once the whole train starts to move, I can go to bed and have a good night’s sleep. I ‘ll wake up in the morning just to get the SD card out of the Nikon.
What about mounts strangling themselves during the night? Ofcourse you have to make sure the scope or lenses are not going to hit the tripod or pier after a few hours of imaging. Ofcourse you have to take care whatever cable spaghetti you have is not going to strangle anything. So… I will hook up the mount onto a timer and give it ample power for a number of hours. Depends on daylight, depends on the declination (hence pier obstruction). The mount shuts down. All other systems like dew heaters, Lacerta, Nikon will keep getting power. According to the Lacerta manual it’s not a good idea to shut it off without power. Always use the power-off menu to do so. So the Lacerta will stay on all night even after the mounts shuts down wondering where his star went. How accurate is it? I use a 180mm focal lenght SkyWatcher finder (8×50) with the Lacerta. I always get stars. Easy. It will guide all my scopes. Yes, even the C11 at 2800mm focus. In theory it shouldn’t. In practice it does. If you don’t want any egg-shapes stars again, buy one now.
Update January 2016: the manual states that you shouldn’t unplug power without shutting down the system first. Allthough I try to oblige to this rule, it happens occassionally that you loose power. I didn’t see any problems as a result of that (yet) A disadvantage I discovered was related to imaging fast-moving comets. It is very difficult to pick out the actual comet on the live screen of the Lacerta, actually tried to do that last night but I did not succeed. Your imaging train or finder scope should be aligned dead center with the lacerta. That is easily done by using an easy recognisable target e.g. Alcor and Mizar. However the party is not on yet at that point. If you succeeded, let me know!
Update May 2017: since half a year I use the Lacerta also as an autoguider for Off-Axis-Guiding. It’s not the easiest job to find guiding stars, but once you have a star and you ran the callibration, it will stick to it. And believe me you will never have seen such sharp images!