sentences:  The Ion has generally been credited with making high-rate-of-fire electropneumatic markers generally available, at a time when electropneumatic markers were considered out of reach of most casual or budget players.The original Ion was released in 2005, and soon soared in popularity, though it was often criticized for being difficult to disassemble and service.Smart Parts addressed these concerns in 2007 with the release of the Ion XE, which allows the bolt to be removed from the back of the marker.