I had a Daisy 717 for a while, nice fun gun, sadly I was forced to sell it so have no idea what they're like long term.

The only die-cast guns I own now are a Record Jumob and a Record Champion, which are both actually ok. There are two main faults with them, the metal gets brittle where it's stressed (the piston and breech are on the Jumbo for instance), and the alloy tends to corrode where it's in contact with steel parts, the screws that hold it together for instance. A reaction gets going where the alloy and steel touches which causes the alloy to turn into a white powder, threads in the threaded holes that the screws reside in can be corroded to nothing over a few years. Sadly I have seen a couple of Jumbos like this over the years. When I rebuilt my last Jumbo I was careful to apply a thread-sealing compound to the screws before refitting, and also keep it well-oiled and greased, which helps.

Some die-cast guns like the Record Jumbo and Champion are good fun and have unusual design quirks, it is the design endears them to me, the build quality is pretty good on the whole and, as long as you take care to stop the corrosion as mentioned above, and don't give them extra stress by firing them without pellets, they should last reasonably well. The steel parts are good, some of the alloy parts such as the piston have steel inserts where they are vulverable to wear, and the barrels are good on these too, with good but shallow rifling to make them as efficient as possible.