Look for clarity on the G string, tone in the high positions, and response to subtle changes in bow speed and pressure. Depending on what you want to use it for, you may want to test projection at a distance, which is not the same as volume under your ear; for that you would need to have someone stand across the room and listen, or have someone else play while you listen from across the room.

As for professional use: it depends on what kind of professional use. The Soloist is in the upper range of student violins. Pros who play in concert halls or other controlled environments (where every little nuance is important), or even people who are auditioning for professional orchestras (where they're competing with a hundred other excellent violinists for one spot in an orchestra), are probably going to want something bench-made with excellent tone quality and response throughout the range. There's a tier in between student violins and what most pros would consider "professional" -- that would be the high-end workshop violins that are frequently used by college-level (pre-professional) students or serious amateurs. Examples would include the MJZ 909, Scott Cao 1500, or Jay Haide L'Ancienne. A pro with a limited budget would likely use one of those.

But many pros also buy a second, less expensive violin to use for outdoor or amplified gigs, where nuances in tone quality are harder to hear and the risk of damage is a bit higher. For those gigs, "good" tone quality throughout the range is enough, and a high-end student violin such as the Fiddlerman Soloist is quite typical. Violins at that level are good enough that they are often hard to tell from a bench-made "professional" violin in outdoor or amplified settings.