The Epos M5 crossover has 3 components for the woofer to achieve a 2nd order (12 dB per octave) filter while the tweeter has 4 components for a 3rd order (18 dB per octave) filter centered at 3 KHz.
The m12.2 on the other hand remains true to the epos tradition of having only one component in the crossover (capacitor for the tweeter). The woofer crossover is achieved mechanically.
The m12.2 is very appealing to tube amp users as the main driver is directly connected to the amp without crossovers to muddy up the sound. Plus it is easy to drive as its impedance dips only to 5.5 ohms at above 10 kHz. (My former speaker goes down to a deadly 3 ohms in the bass region.)
The mids are sweet and the treble, very detailed and the bass can rival floorstanders as noted by Jetok. I fell in love with these speakers the first time I saw/heard them and eventually took a pair home. The m5 could suit smaller listening rooms but the soundstage of the m12.2 is more vast compared to its smaller brother.
Here is a tweak I did to my m12.2 which can raise the treble performance a notch higher.
This is easy to do as the tweeter grille/cover is only held in place by the tweeter's magnet.