You need to have room for them. You need to have sufficient power for them. Beyond that... a true audio classic and a great speaker. Magnepan will rebuild them if necessary I believe (though not cheap.. and expensive to ship).
A good source of info is: http://www.integracoustics.com/MUG/MUG/
The ribbon tweeter on them is simply amazing. The maggie bass is also extremely nice.
mdl.