Taking care to get the aluminum extrusions perfectly aligned with each other and using a file to true up the joining edges will make a big difference. When all else fails, a piece of Scotch tape across the joint of the PC board strips will help. There are also some slide tightness adjustments on the back of the readout module, but be careful with this, as too loose will cause readout errors.
I attached my Wixey DRO to the bottom of my Unifence rail with short pieces of 1/2" square steel tubing cantilevered out from the underside of the Unifence rail. Then the Wixey extrusions were attached (upside down) to the bottom side ends of these pieces of square tubing (but make certain that you install the PC board strip rightside up). I cut the piece of steel with the rounded ends that came with the DRO in half and attached one piece to each side of the Unifence casting, drilling and threading holes in the casting for attachment bolts, positioning these pieces to align perfectly with the magnets on the ends of the DRO module. I bought an extra Wixey extrusion and PC board strip so I could use the DRO on either side of the saw blade as well as either side of the fence. Moving it from one side of the fence to the other does require re-zeroing it with the fence touching the blade, but that's all that is necessary, and just holding in the button on the DRO module for a couple of seconds, with the fence touching the blade lightly, does the re-zeroing. The magnets on the module do a great job of holding the module attached to the fence casting, if the magnet to metal connection is parallel. Having the DRO extrusion running the full length of the 52" Unifence rail also keeps the readout module from falling off the end of the extrusion if you should move the fence too far past the blade slot as well.
I like the ability to switch between Metric and Imperial, and the ability to have absolute readings as well as incremental readings. I've found that I can cut a board to a specific width, then move the fence and make another cut, then move back to the first position and make a second piece at this same original width, and both cut pieces will measure the same within just a few (.003-.007") thousandths of an inch of each other. I almost never use the Unifence ruler scale any more.
My Wixey DRO is over 10 years old, bought when they first became available, and I've not needed to do anything to it, other than change the battery. I occasionally have fine sawdust get into the gap between the display and cover glass, but just a blast of air, without dis-assembly, clears it out.
Charley