Kamacite and Taenite
Kamacite and Taenite are both Iron-Nickel alloys found (on Earth) only in meteorites. Kamacite's composition is in the 90:10 to 95:5 Fe:Ni range. Taenite's composition is from 20% to 65% Nickel.
Kamacite, in particular, can form massive crystals. A kamacite crystal listed in table 1 here had dimensions of 0.92x0.54x0.23 meters, and a mass of 303 kg; plenty of material to make a whole batch of swords. Finding these crystals means that you have found a pre-mixed alloy. There is no longer any need to smelt to mix the alloy. The crystal can be directly worked into a sword via the normal methods. The melting point of both kamacite and taenite is not significantly different from iron, so normal, time-period appropriate methods of swordmaking would be valid.
Hardness is the resistance of a blade to strain. That is, when a force is applied, how resistant is the material to deforming. A harder blade will cut through a softer one (or wood or bone) without getting blunted.
Both these alloys have a hardness advantage over regular iron. A study of 22 siderites (Iron-Nickel meteorites) reported on their hardness in Table 1 here. For a comparison, we can use this study of wrought iron sampled from 10 bridge built in Massachusetts in the 1800s.
The average Rockwell B hardness of 24 meterorite samples is 81; while the average from 53 bridge components is 58. The 95% upper limit for the bridge iron is 72; 92% of the meteorite samples had a hardness greater than this. For a comparison to more modern materials, matweb.com's database has information of 176 types of high carbon steel. The average Rockwell B hardness is 95.7 over the range 43-100.
Rockwell B is a hardness test for softer materials, so it doesn't scale well to harder materials. For example, the difference in theoretical hardness between 95 and 100 is much larger than the difference between 40 and 50 on the Rockwell scale. For a better high hardness test, the meteorite study includes the Brinell scale as well.
The average Brinell hardness is 169, but with an upper limit of 330. 9% of the samples have hardness over 230. This variance in hardness may be a result of the shocked vs. unshocked nature of the crystals. Unshocked crystals evidently have hardness about 50% higher, according to a Wikipedia statement that I cannot verify.
Unworked iron has a Brinell hardness of 110-120. This is the base material from which a sword is made, so a kamacite alloy can start two or three times harder than pure iron.
The standard measure from blades is the Rockwell C test. The Rockwell C hardness for three Damascus steel blades from ~1750 are given as 23, 32, and 37. This chart converts those values as 240, 300 and 340 on the Brinell scale. A summary chart (Graph 1 here) shows average example blade hardness from 8 swords that convert to 130, 170, 180, 190, 210, 260, 400, and 440 on the Brinell scale.
For modern materials, cast iron has a Brinell hardness of 183-234 and high carbon steels from 163-600 with an average of 262 (over 207 different types). So it is possible to find a meteorite alloy that is harder than some modern high carbon steels and as hard as high quality Damascus steel blades. Perhaps 10% of the iron-nickel meteorites you find will be of the un-shocked high hardness variety. A modern tool steel forged into a Damascus type blade had hardness of over 700.
Strength is the ability to withstand deformation. The integral of strength over deformation distance is toughness. While a hard blade might not deform upon being struck against a stone wall, it might fracture. A tough blade will deform (getting notched, or bent slightly) but won't fracture. The data for stress-strain curves for meteorite samples is not available (to me, at least), so instead of toughness I am using strength at comparable strains.
The Gibeon iron-nickel meteorite was drawn into a rod with a tensile strength of 392 MPa and a compression strength of 373 MPa. For a sword blade, compression and tension strengths would be similar to each other. For a raw meteorite alloy, the kamacite meteorite found in Canyon Diablo had a compression yield strength of 424 MPa with 0.2% compression (that means it only deformed by 0.2% of its initial size); tensile strength should be similar.
The comparisons here are to modern cast iron, with a tensile strength of less than 276 MPa. High Carbon steels have a range of tensile strengths from 161-3200 MPa with an average of 1010 MPa over 219 types. The ratio of tensile to compression strength can vary by application.
Manually puddled wrought iron, made and reported in the 1920s, had tensile strengths around 165 MPa at 0.2% tension. The bridge samples averaged yield stres of 230 MPa; all samples yielded below 0.2% tension. An investigation of iron products made in a replica of a 10th century forge had yield stress from 300 to 500 MPa with yield elongations between 0.05% and 0.4%. Ancient Wootz steel swords were found to have yield strengths in the 800-1500 MPa ranges. Modern steels forged into layered Damascus steels were found to have yield strengths around 1200 MPa at 1.3% elongation.
Overall, we can see that the compression strengh of the meteor iron is lacking in comparison to modern materials or the finest Damascus steel, but competitive with medieval forge products.
The alloys found in iron-nickel meteorites had properties that would have made them competitive as blade making materials. For hardness, un-worked meteor crystals had hardness equal to the finest Damascus steel blades, close to the finest of any blades, and significantly higher than wrought or cast iron. This material is un-worked; the raw alloy has a hardness advantage of two or three times on un-worked iron. Presumably there is quenching and tempering process that can increase the raw material's hardness by another factor of two or three, just as ancient steel blades are up to four times harder than raw iron.
Toughness is greater than the iron products that would be common in everyday use, but not as great as the best steels available. Toughness is equivalent to iron sword products made with 10th century technology.
Overall, I think that you could reasonably expect a 'just right' Iron-Nickel alloy meteor to contain large, pre-alloyed crystals that could be forged into swords. This alloy, if annealed just right (through luck, the assistance of the Gods, or however the smith acquired the right knowledge) would make a blade strong enough to be usable, but harder than anything available until the 19th century.