After anolysis, I have concluded that the weapon as-is... is sub-par. It's steel-tier, cannot be smithed unless you have Arcane Smith (by which point you'll probably be cranking out battleaxes or any other weapon of higher-tier material), it's not an option for onehander players, is on a slow-to-swing Battleaxe, and its enchantment damage magnitude is low-level, as I said earlier. Unless you beeline straight there out of Helgen, it's gonna get outstripped quickly.

It is disenchantable, however, and retains the fiery soultrap effect, so Twin Souls is not needed to gain its benefit. It does not, however, benefit from the Fire Enchanter perk, which means as a damage-dealing enchant, it will eventually be outstripped by straight fire damage. There may be limited use for twohanders and bows, but for a onehander who can just quickly whip out the Soul Trap spell with a much longer duration and still benefit from the stronger straight elemental damage enchant, that becomes moot.

I am a new comer, so if there is a better one. Correct me on it. I did the daedric quest the house of horrors, and this might come in handy for the OP, as well. As a reward, the daedric lord gives you the Mace Of Molag Bal. It has the soul trap spell on it, as well as two other enchantments I think. Stamina damage and Majicka damage. (three enchants)

The up side is it's a wicked weapon, and since it has the soul trap spell already. You can charge your weapon, as you use it. Theoretically.

The downside is its a mace so a slow swinging weapon, But once you get your critical strike, in one handed weapons. The soul trap is like clockwork.

Of course it's all in game legal.

Well everyone is entitled to their own opinion of course but I think you're selling it quite a bit short. The weapon itself is weak being Steel tier but virtually no one aware of it goes for the weapon just to use it - most people disenchant it to get the effect to be known for enchanting all sorts of other weapons for their own use or by followers. Basically, if you want to use a soul trapping weapon to fill soul gems, why not get a free 10 points of Fire Damage on every swing on top of the soul trap effect?

The weapon itself is nothing, its the disenchantable fiery soul trap thats worth acquiring. Its also better than basic soul trap, thats the point. If you're going for soul trap on weapons anyway why not get a bit of fire damage as well, two for the price of one?

Not everyone is a mage or is into one handed (and even if they are they'll probably be carrying a shield in the other, I for one rarely bother casting and never during combat)

I dual-wield crafted katanas (first steel, then later ebony). The right hand one is enchanted with Fiery Soul Trap, and the left one is enchanted with Frost (whatever it's called, not in game right now to check). These weapons get me through the entire game; before my Smithing is advanced so I can improve enchanted weapons, I don't enchant the steel katanas before being able to improve them to Superior. At that point I enchant them as above. These will get me to whatever level it takes to make Ebony katanas. Usually at that point I will also be able to improve enchanted weapons. And then, I don't really need anything else....

Blackjack Davy,

Damn your eyes! (or some other equally vindictive saying will do here)

I got that mace and sold it! True, I've got so many available enchantments that I struggle to put two on one item at times but...firey soul trap? Aargh! It's like finding a lovely glittery enchanted daedric great sword lying around in a dungeon. Even if you've got to creep home because you're too overloaded to run or fast travel, it has to be done.

Blast, blast and even less savoury epithets!

I shall now go and weep into my beer...I could be some time...you may not hear from me again...firey soul trap?...heaven...and I don't have it...

Well, it's a battleaxe not a mace, and if you're on PC you can console one in since you had it once....

Oh. You're on a console box aren't you? I suppose it would be WAY too far back to go back to that save?