Don't get pop rivet tools at the big box stores, they generally don't have top quality tools of this nature. Talk to a local sheet metal worker and find out where they go for their unique tools. (I'm trying to remember the name of the place around here, I believe it is a chain of sorts..)
Mine are all older so not sure if they are still available/USA
The top 2 sets are from the United Shoe Machine Company Pop Rivet Pliers. note that there are no "extra" bits screwed into the frames, These are made to size. this means the clutch mechanism for the smaller shank rivets works better (the "one size does all" often take one more squeeze to get to the final pop on the smaller shank rivets)
The next one down is a Marsen "Klinker"
And the last one down has the stickers worn off, so I don't know who made it...
Note all these have aluminum bodies compared to the stamped sheet metal bodied rivet tools you find in the big box stores... Those may work fine out of the box, but will not last.
If you want to buy used, that's OK, but also take a few rivets with you and test them though. they do wear out. if it take more than three squeezes of the tool to get a pop, it is worn out or junk to begin.