I am looking forward to trying this card out. While it's still no Machete, I think that this could be a good second weapon for a lot of Guardian investigators.
Let's get one thing out of the way - this card does take up 2 slots, which is not really great. However, most investigators that aren't Mystic investigators don't end up using both of their arcane slots anyway, so the arcane slot requirement for Enchanted Blade isn't super prohibitive for them. That may change going forward as arcane slot assets become more common for other classes.
I think the best way to measure this card's effectiveness is to look at it compared to some other level 0 Guardian combat options:
.45 Automatic: The .45 Automatic costs one more resource and has one more ammo on it than Enchanted Blade has for charges. However, Enchanted Blade can be used without spending a charge to do a slightly weaker attack, where the .45 Automatic always has to spend an ammo, which can lead to using ammunition to inefficiently do 2 damage to an enemy with only 1 health left. Enchanted Blade offers more versatility, which in some cases can get you further in a scenario, and its charges offer a greater bonus than the .45 Automatic can provide.
Survival Knife: Both offer a regular +1 fight action with a secondary option to do a +2 fight action that deals +1 damage. The special fightt ability on Survival Knife doesn't cost an action since it's a ability (so you can theoretically attack 4 times in a turn for 5 damage total) but the downside is you need to be attacked by an enemy during the enemy phase to use it. Enchanted Blade may cost 1 more resource, but the ability to use a 2 damage attack without having to wait for an enemy to attack you makes it much more practical to use.
.32 Colt: it is card to compare these cards since they do very different things - Enchanted Blade gives you additional for fighting with the occasional extra damage while the .32 Colt gives you 6 attacks that do +1 damage with no bonus. In my experience, I find .32 Colt hard to use with anyone who isn't Mark Harrigan, because high-health enemies often have high fight checks required to hit them, and so the .32 Colt sometimes has trouble actually hitting the enemies you'd want to use it on the most. Enchanted Blade does not have this issue, since its charges make your attacks do a total of +2 and +1 damage, meaning you're more likely to hit when you really need it.
Knife: Enchanted Blade is basically a Knife that can have its second ability used 3 times instead of 1 time. Now, I don't use Knife a whole lot, but part of that is you have to throw the Knife away to make it more powerful. I think that the 3 charges actually makes Enchanted Blade much, much more useful and I think it's worth paying the 2 extra resources to get the 2 extra uses.
Ultimately, I think that Enchanted Blade is most at home with Guardian investigators who will want to use it as a pseudo-Machete until they get their real Machete out. I think that Enchanted Blade can also be used as an off-hand weapon to cover some of the blind spots of the Machete - specifically, when you're engaged with more than one enemy or you need to deal more than one damage to a monster not engaged to you.
I think that most Mystic investigators are going to not get quite as much use out of this card, as their arcane slots are more valuable and they generally tend to avoid tests. It may be situationally useful for them, though.