Just an opinion.
What I like: There is not enough healing in the core set, so often times when you get low on health or sanity, you better book it or pray. The cost is reasonable, it doesn’t take up a slot, and you can use it on other investigators which could turn you into a little mini-healer which Agnes will love so she can ping a couple more times. The fact that it heals horror and damage is functionally useful. The will skill icon is great for both Roland and Skids right now, as they don’t have a very fun time with will based treacheries. Not needing a skill check to complete (medical texts) or a check to make it better (liquid courage) is also good in some situations.
What I don’t like: The action economy with this is abysmal. I understand, you’re not winning if you’re dying, but to just use it once you’ve spent two actions not making progress. I never feel like I have enough time to play it in solo, and even in multiplayer either the threats have been tackled evenly so there isn’t a dire need for it over something else or the situation is already so bad that spending those actions to recover won’t really help much. The scenarios are just too short in my eyes to warrant using this in most cases.
What it needs: Honestly, first aid needs more investigators like Agnes who care about taking some sort of damage or horror. It also needs other healing cards to stay out of the game. I would gladly take the risk on liquid courage over this, because healing two for a single action is much more reasonable even if it is only horror in that case. As time goes by I feel like healing options will only improve, and unless they are using first aid as a benchmark and everything else gets a risk or negative involved, first aid will fall to obscurity.
Scaling: Here’s where this card shines however. First Aid as it stands has the same level of power in all the difficulties, which gives it a slight edge. With no test needed to make it work and no test needed to get a benefit, it gets more reasonable as you up the difficulty. Easy and standard, I’m waiting for a better option but in hard and expert, this does seem a bit more reliable.