The one month (Continouspass or the Flexipass with Xdays in a month) means you can activate it on the 15th August and travel as much you like till the 14th September so yes a one month pass covers you traveltime in Europe.
Note that Traintrips in East Europe are pretty cheap and normal tickets are cheaper as the “value” of a travelday of the pass ;)
Oops, I missunderstood the question...
It all depends on where and what trips you want to make, but probably the best way is to buy a pass with a nr of passdays for really long trips and from/to your home and pay locally for short trips, Or f.e. in summer in CZ and SK and all year in PL there are also very cheap local passes for 1 week or a nr of days-limited to special train companies.
If you intend to mainly visit old Yugoslavija-Bulgaria, then forget the pass. You will very often turn to the bus due to lack of trains running.