For Siege, the question is Will you ever have taming? If not, go for it man. As long as you've got the stable space (limited amount, esp non tamers), vollems are fun. BUT, if you are a total pet ***** like me, every space counts. Since vollems have the same stat range as nightmares, a tamer would do better to get the mare because they are free and you get to pick one with optimal stats / resists. IF YOU HAVE NO INTENTION of taming though, vollems are great. you will still need to train them just like any other pet. They are cute little hellraisers after that.