If you want to learn about the benefits (and science) of NMN in anti-aging/longevity, read "Lifespan: Why We Age_and Why We Don't Have To." The author Professor David Sinclair goes into great detail about the benefits Nicotinamide Mononucleotide.
As a someone who desires longevity (or healthy aging), I didn't hesitate to snatch up Neurogan's Nicotinamide Mononucleotide (NMN) Supplement. To understand what it does for my body/health, I require labs. Labs I don't have. So, again, I have to refer you to the book I mentioned earlier (and no, I'm not getting paid to plug it).
As for the supplement itself, it has a minty and tart taste. I've experience no negative side effects. On the contrary, I feel great. Do your research, and maybe you'll find this product worth trying.

I'm not going to go into the benefits of taking an NMN supplement as you age -- you already know those if you're here. I do think it's a beneficial supplement and helps those of us over 40.
So let's get to brass tacks here.
The taste? It's not horrible. It's not great. It's not going to cause you to gag or anything. It's basically as described -- a sour apple/mint flavor. What you need to expect is not a candy/sugar form of "sour apple" you're used to -- it's just kind of sour apple/minty. The taste shouldn't hold you back even though it doesn't taste like Jolly Ranchers or anything.
My other nitpick? The dosage size is 1 ml. The dropper inside the bottle is marked for 1ml. But for some reason, no matter how much I tried, I could only get that dropper to fill up to the .75ml line. I tried for over 10 minutes to get this thing to fill up that recommended dosage line and couldn't get it there. I finally got frustrated and took the .75ml and then went back to take a .25ml dose. That was annoying. Maybe it was just my bottle or dropper as I haven't seen anyone else complain about this, but it did happen to me.
NMN is a pricey supplement in general so I'm not going to complain about the cost here. I will report back later this month if I notice anything exceptional or terrible as I continue using this.

I like the anti ageing aspect of NMN and I really like that this is a liquid which feels more available to the body. I will say this isn't the best tasting drop I have ever had, but it's medicinal so you deal with it. Anyway, if it keeps me looking younger than I am, I am all for it. High dose also doesn't hurt.

Great taste and absorbs quickly into the body
Just started taking and seems to be working as advertised

The description of these drops is a bit erroneous - the bottle clearly shows that there are 60-1ML servings. That said, the label further clarifies that the recommended dose is 1-2 servings in the am, and 1-2 in the evening "for best results." No big deal, but I thought I'd point that out.
This stuff is purportedly "apple" flavored. Not sure if I totally agree, but it's a bit sour and not totally pleasant, so yeah, maybe it's apple flavored. As a sublingual drop you put 1 ml (measured with an included dropper) under your tongue and let it sit for 45-60 seconds. Not terribly hard.
NMN has a host of purported health benefits, and I've been taking it for a while as a consequence. I do tend to believe that sublingual is the way to go, but I also take a resveratrol capsule with it to increase absorption. So if you don't normally take resveratrol do a little research and consider that as well - at an increased cost, of course.
I do like that the bottle clearly identifies this NMN as made in the USA, in a GMP facility, and that it's non-GMO (it's also vegan but I don't care about that as much as some readers might).
At 250MG/serving, this is a bit less than I'm used to taking - presumably that's why a bottle lasts 30 days, even though it's got 60 servings. So this costs around $40 for a month's supply - maybe a bit pricey, especially if you need to add resveratrol to your supplement mix as well. I'd recommend this, but caution about the price.