I recently switched to the Harrow Spark after several years using the Black Knight Magnum Corona. The primary difference between these racquets is the lightness of the Spark. The Corona is, in my opinion, a fairly standard racquet in terms of weight and balance. The head is almost completely circular while the Spark is more oblong.
There is, of course, a trade-off with a lighter racquet. The Spark is a very “maneuverable” racquet, meaning you can hit the ball with a compromised or improvised swing and don't necessarily need a full backswing to make good contact. However, to generate power you need ample racquet head speed. It took me a few weeks to adjust to this difference; the Corona was heavier and thus more powerful. Overall I prefer the freedom afforded by the Spark. It is much easier to dig the ball out of the back corners, and to hit the ball when it’s behind you (or otherwise non-ideal positions). Having to generate racquet head speed is also a good thing for shot consistency and accuracy. I would recommend it for players who feel their current racquet is sluggish or difficult to control.