Upon examination, this RJ-11 Sensor Breakout has virtually no electronics on board. The only active component is the voltage regulator. This means that all the active electronics and thus the voltage and current limitations are set by the actual Limit Sensors. (ie: Creltek 343RT). I mention this because the available documentation does not make this clear. It goes into some discussion of setting the voltages, but it's not too clear exactly what is going on. The Sensor Breakout has a sensible design and there is virtually nothing that can go wrong with it.
As for this breakout's physical characteristics, I was able (with only a minimum of file-work) to set it up in a card slot opening in the back of my mini-ITX computer case. Yes, it needed some custom made angle-brackets to hold it fast, but the RJ-11 sockets stand proud of the slot with a perfect fit, no gaps.
Awesome to hear that it fits nicely in your case slot. :) The RJ-11 Sensor Breakout board does have a fairly robust design. It is worth noting that a newer version (v1.2) of the board has been released since this review was written, and the outputs are now dedicated open-collector transistor drivers with an optional (removable) pull-up resistor pack, as well as noise-reduction circuitry on the inputs. The design is even more robust (in my opinion), and allows these sensors to work with voltage ranges on your motion controller inputs up to 30V. Dimensions of the board are very similar, and the width is the same.