The only drawback to mix n match cassettes is that the shift gates will be in the wrong place. What puts the Glide in Hyperglide is that the sprockets are phased so when the chain comes through the shift gate it's rollers are positioned exactly (phased) to engage the neighboring sprocket. When the gates aren't in the right place the chain may climb onto the tips of the teeth on a shift then only drop in when you pull it forward causing a small skip.
pre-index riders are familiar with this, and with your mixed cassette you'll feel it too. It's no big deal under you like to shift under load.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.