I have some experience with the Unistar and the MG2, using a FS-102 or a 120ED OTA. With both mounts, the imbalance caused by a 2" diagonal, a fairly heavy eyepiece and the finderscope (all with a CG above that of the tube itself), tend to make the OTA rotate when it is pointed nearly vertical.
The DiscMounts tilt-in saddle is offset about half an inch downwards in order to balance better. The altitude axis centerpoint thus lies a bit above the tube centerline.
Further regarding the DM6 (and the Berlebach Planet), some points I've noted and experienced, in no particular order:
The extension really is necessary for use with an even moderately long refractor. The DM extension (to me and to my engineers eyes) looks like a design that would not be particularly stiff torsionally, but in reality is is quite stiff. I can't note any difference in mount damping time with or without the extension (loaded with a pretty heavy 130 mm f/6.3 triplet).
The handle is nice to have. I got the angled version to avoid it being too close to the focuser, but in retrospect the straight version would have been better because it does not interfere as easily when viewing targets with higher altitudes. I've seen pictures where people have tried to avoid this problem by turning the saddle upside down, but then the saddle offset is wrong vs the scope center of gravity.
If you plan to use the DM mount with a tripod other than a DM, remember to order the "interface disc" (round spacer) to go between the tripod metal top and the mount metal base. I fastened the disc with double sided tape to the Planet top plate.
The leg angle of the standard Planet is much too narrow for my liking (with an offset load such as on any " side-mount head". I have had a Berlebach UNI 18 L for about ten years now, and I particularly like the wide stance of that tripod, when used with the largest tray available. The Planet comes with a fixed spreader, but I ordered mine to be delivered unattached, so I could choose the leg angle I wanted before fastening the spreader. I fastened it as high as possible, while still allowing decently easy removal of the tray.
Double leg clamps are nice to have, as wooden tripods swell and contract with humidity changes.
As are the rubber feet, if using the tripod on concrete or a wooden deck. Or storing it on a wooden floor...
The Nexus WiFi telescope interface can be highly recommended, and it sits very nicely with velcro (or with its own mounting plate) on the rear plate (opposite the scope) of the DM6. Works flawlessly with Sky Safari. I still use the Argo Navis when the temperaure is too low for iPad use or the site is too dark to risk ruining my night vision with the iPad, but other that that, Sky Safari and Nexus really are a great combination.
I chose the DM6 over the T-Rex and various AYO-models because it felt like the mechanically least complicated, and thus probably most rugged alternative. I fully beilive I would have been happy with any of the above mounts (when the Giro I had, and still use with ligher scoped, proved too weak for the inteded use).
I haven't had my GEM out for almost a year now - the whole time since getting the DM.