This is a false statement IMO. My first monitor was an Ornate Nile Montior and he is great, he isnt agressive at all and eats like a garbage disposale. Nile Montiors are good, begginer or not. You still need to take proper precautions tho before purchasing one, keep in mind they eat like crazy, you will be spending alot of money on food, you will need a big enclosure when they get older, and just remember to hold them alot and they will be fine, mine isnt agressive at all.
Dont exclude a nile montior from your decision.
FYI they arnt lazy either, mine is VERY energetic.