The mistake is buying for the weekend you imagine rather than the one you'll actually have, so you end up with something huge and complicated that gets used three times a summer and resents you the other fifty. The weather you actually get, the number of people who actually show up, and how much space you actually want to give up to it matter more than how good the thing looks folded out in the shop.
Whatever you choose will spend most of its life outside, so think about how it ages before you think about how it looks on day one. Metal finishes dull and spot with rust where water sits, especially around welds and screw holes, so anything left uncovered through a damp winter will look five years older than it is by spring. Cast iron and heavy steel take this better than thin pressed metal, which dents and tinnies underfoot or under a dropped log in a way that tells you exactly what you paid for it. A cover earns its cost back fast. Wipe down grates and bowls after use rather than letting grease or ash sit, and anything with a gas line or electrics should get checked for corrosion and loose fittings at the start of each season, not halfway through a dinner when it won't light.
None of this is the right choice for every garden, and it's worth being honest about that before you commit. A serious wood burning fire pit wants real outdoor space around it, not a balcony four feet from a neighbor's washing line, and a lot of strata rules and rental agreements ban open flame outright, so check before you fall in love with one. Gas heaters give you instant heat with none of the smoke but they're hungry for fuel and loud when the canister runs low mid party. If you're renting or moving within a year or two, go lighter and more portable rather than buying the heavy built in version you'll have to abandon.
In the shop or the moment it's delivered, check the weight is where it should be, a heavy stable base, not a cheap top bolted to flimsy legs that wobble when you knock the table. Push down on grates and shelves to see if they flex. Look at welds for rough or sharp edges, and check wheels, if it has them, actually turn and lock. For sizing, measure the clear space around it with at least three feet of nothing flammable on every side, more for anything with an open flame, and remember heaters throw warmth in a circle, not a room, so one in the corner of a big patio is mostly heating the fence.
Let metal cool completely before you cover it, or you'll trap moisture and rust it from the inside out.