The iFeel Mouseman is simply a modified MouseMan optical mouse. That means it has the same 4-button layout, right-hand specific ergonomic design, blue LED power light, and the Agilent imaging unit also used by Microsoft, Apple and Kensington.
The MouseMan is smaller than the Intellimouse Explorer and actually fits my hand quite nicely but for traditionalists looking for an ergonomic, comfortable, but smaller mouse, Logitech also has the iFeel Mouse which is based on its Wheel Mouse Optical. The only differences between the MouseMan Optical and iFeel version are the new, slightly iridescent exterior, exclusive USB support, and an Immersion-designed vibration unit.
Sizing up the competition
Don't stare at the LED!
Logitech's iFeel mice use Immersion's high-fidelity Inertial Harmonic Drive (IHD) engine and the TouchSense API to produce vibrations in the Z-axis. Compared to Sony's Dual Shock technology, the IHD offers greater precision and detail but is weaker, and is unable to physically move your hand. Dual Shock controllers have one motor attached to a light mass and another motor attached to a heavier mass. By spinning the masses in different sequences, a limited number of "on/off" effects can be created.
The iFeel technology is much closer to true force feedback technology. Developers simply need to describe a wave function including variables such as frequency, amplitude and duration of the feedback and the hardware takes care of the rest. Thus, instead of Dual Shock's simple on/off feedback, the iFeel can crescendo, fade, and combine multiple effects to simulate a variety of responses including quick pops and different textures. The wave function approach affords a subtlety of effects but this is both a benefit and a weakness, as we will later see.
By only providing vibration feedback rather than true force feedback that can push and pull your hand, Logitech was able to physically integrate this technology into the mouse without needing a fixed mouse pad or a huge price premium. In addition to the feedback features, iFeel mice also function as standard Logitech optical mice.