Tube amps tend to produce heat and monoblocks will heat up a room faster than a stereo amp, as they generally have more output tubes (but not always).
Monoblocks mean you will need to buy twice the number of tubes. This can be an expensive difference.
Monoblocks are twice as powerful as a stereo version of the same amp, but if you can get away with lower power, you are better off, as additional output devices mean a more complex circuit and less pure sound.
Monoblocks tend to burn more electricity (because there are two of them).
Monoblock amps can be positioned much closer to the speakers, thus allowing really short (and thus cheaper) speaker cables.
Monoblock amps can be work if, like most of them, they do not autobias. My monoblock / stereo tube amps autobias, so this is not an issue for me.
Monoblocks tend to be more difficult to resell, as they cost twie as much as a comparable stereo amp (there are factors that make them easier to sell, but this was not intended to be a tutorial in economics).
About tube amps in general, it is a very expensive sport, as a tube amp that can truly control woofers in dynamic loudspeakers (as opposed to planars, electrostatics, etc.), which is what most people run, is very hard to find, and the few that can are very expensive (like $10k+ retail as an entry-level point, with $25k-$30k retail being more typical). Your speaker is very efficient, but drops below 2 Ohms in the bass and has a nasty phase angle at 20 Hz., meaning only a small handful of tube amps will work with your speakers. One relatively available and relatively affordable tube amp that can drive a 2 Ohm load is the Sonic Frontiers Power 2 stereo amp and Power 3 monos. VAC's Renaissance amps and the CAT amps can as well (the CAT's are the best I am aware of in this regard), but are more expensive.
