Got a Carbon in the end a few days back, early days yet but between it and Pyaramid there are a lot of different features but also some very similar limitations. Both really only can have 1 "song" in memory at a time in that you can't really do a whole seamless live set of different parts, which I find kind of strange given that both devices are aiming at live use. To elaborate on this a bit, both devices only have 1 set tracks in memory at a time, 64 on the Pyramid and 6 on the Carbon, on the Pyramid you have "sequences" which are mute groups of these 64 tracks, on the Carbon you have 6 scenes which are variations on these tracks which can include length, startpoint, transpose etc.
Both of them can get a fairly broad range of variation from these tracks, and both offer fairly good real-time editing and manipulation of the data in these tracks, but you cannot have tons of different patterns in them at a time, so for me I feel they are both best used for composing rather than extended live sets.
I think they are both very good sequencers, both have some quirks, but both can be very inspiring to use and both are well thought out, the Pyramid is probably better suited to rhythmic and experimental or complex stuff, the "P-lockable" FX and recording of CC's, euclidean modes and drawing control data using the touchpad etc are really innovative, note and chord entry are very simple right on the surface. The Carbon is much simpler but geared a little more hands on manipulation of the actual sequences and they become more real-time tweak-able which lends itself to nice odd-meter acid and techno type stuff very well.
I sold my Pyramid to buy the Carbon, I do not regret it, as Carbon seems to offer more what I am looking for at the moment, but I would not rule out getting a Pyramid again in the future, Squarp customer service is second to none, and they seem very committed to improving the Pyramid and adding lots of new goodies at regular intevals.