iv been using mine for bout 6years now and id fully recommend it as a sequencer for building beats..so jammable and user friendly...its like playing an instrument...truly..
the downside is the fact that its pretty old n it cant hold nearly as many samples as a pc..also the filter is very basic but does have a cirtain crunchyness that cant be achieved by anything else IMO
second hand you shouldnt be looking at anything over £500
:)