Regarding robustness I'm not sure what JBC employs to prevent over insertion of cartridges but Pace has their key system that won't allow the cartridge to physically go any deeper into the handpiece beyond a point.
It doesn't put pressure on the connector but even if it did there is an oring and washer that sort of float the connector in the back of the handpiece.
Hakko's sleeve system is a inferior plastic quality handpiece and cartridge swapping system that feels quite crunchy, they have moved away from it as of the FX971 but still looks plastic.
Here is a breakdown of the Pace TD200 handpiece. The handle body is one piece of machined aluminum which doesn't make contact with cartridge body so remains quiet cool in your hand. It sort of acts like a heatsink with an air gap. Everything appears hand assembled so can be dismantled resoldered or repaired.
Anyway buy whatever does it for you or your budget etc. Note Hakko and JBC need specific stations to run tweezers.
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