I have previously used Thomastik Spirocores in several different gauges, so that was my reference point for comparison. The Prestoflex strings do a similar job and are likely to appeal to the same players, but they have a subtly different character. They have good volume and a lot of sustain and growl when played pizz, with a nice clear high end that is quite distinctive. I like that they remain clear toned and sustaining as I move up the neck into thumb position.
With the bow they have a fairly bright tone, but they're easy to control and play cleanly. Though their strong point is that modern jazz pizzicato tone.