My first two shortwave radios did not have tuning knobs. I've since acquired radios with tuning knobs, and I learned a few things that seem worth sharing.
Some shortwave radio reviewers consider tuning knobs a must-have feature, whereas I consider them nice to have. Lately I've been using direct frequency entry to listen to specific broadcasts rather than scan the bands.
* The knob's step size on a digitally-tuned radio is an important characteristic. My Tecsun PL-350, for example, has a fast and slow tuning mode toggled with a button. This provides a 5khz or 1khz step size for shortwave tuning. A Tecsun PL-200 only allows slow tuning with a 1khz step size for shortwave.
* The feel of turning the knob one notch or rotating it quickly will vary among different models. Sometimes the knob doesn't stop within a notch after rapid tuning on the Tecsun PL-350, and the frequency of the radio may change unexpectedly. The knob on the PL-200 doesn't provide sufficient responsiveness with rapid turns, so it may only advance half as far as you expect.
* Some radios feature a 2-in-1 tuning knob, with an outer knob for fast tuning and an inner knob for slow tuning. I really like the 2-in-1 tuning control on the analog-tuned Eton FR250, where the ratio between the two knobs is 4:1. I understand that the tuning control on the digitally-tuned S350 and S350DL radios (Tecsun BCL-2000 and BCL-3000) is similar.
* Tuning dials (that more closely resemble a volume dial than a tuning knob) are more prone to drifting. The Countycomm GP-4L (Degen DE202) has a tuning dial. Due to this dial's small size, it's difficult to get the right tradeoff for fast and slow tuning. Two large shortwave bands combined with the dial's fixed range makes changing between bands annoying, because the frequency is determined by the dial's relative position. A radio like the Kaito WRX911 on the other hand is analog-tuned with a tuning dial, but displays the entire band with a tuning needle so the user has an idea of how fast or slow to turn the dial. In my opinion, this provides a better experience than a tuning dial on a digital radio.
* While reading shortwave radio reviews, I read about "chuff" which is an effect of tuning a digitally-tuned radio. My understanding is that chuff is the brief silence between frequencies, intended to mute an undesirable radio noise. Some radio enthusiasts figure out how to disable the muting so the sound is continuous when tuning with a dial.
I hope this is useful (and also correct)! Feel free to leave a comment about this topic or to suggest other radio topics I could write about here.