I've used both...but maybe three decades ago! At no more than twenty yards range.
From memory in my rifle, a BSA Martini, there was no accuracy difference.
The good bit:
In a LONG barrel rifle the powder is all burned. The report is quieter than a springer air rifle.
So, re the above, you get low noise shooting without need for any moderator.
They hit the target like a hammer. Again far more power than any s1 air rifle.
The bad bit:
It a solid bullet. It doesn't expand. It shoots clean through a squirrel.
It has ZERO "stopping" power and IMHO was less effective at "stopping" body shot squirrels than did my standard 12 ft/lbs BSA Airsporter Mk I .22 with Eley Wasp pellets.
So to sum up it's good for short range vermin IF you use well placed head shots NOT body shots.
Yes, it saves you buying a s1 air rifle, or indeed a 12 ft/lbs air rifle but it does kill any better and what I experienced not in fact as well.
Would I use the OP's combination a Z Lang or CB Long for garden squirrels, magpies, pigeons at twenty yard ranges?
No I'd use what I do now a 12 ft/lbs BSA .22 Scorpion T-10 PCP ten shot repeater air rifle.
Hope it helps. The ONLY benefit IMHO is it saves you buying a repeater, magazine, PCP or single shot springer air rifle.
But with that benefit is the handicap that it is a solid non-expanding bullet so it WILL shoot clean through.
Oh and it's not as accurate as a GOOD PCP air rifle...from memory.