They may not be super high quality in terms of feedback, mud/slurry formation, dishing resistance, etc etc but my guess is that the grit rating is reasonably accurate.
In my experience, they are not. I purchased some of these from Amazon under the "Amazon basics" label no less. Meaning it's an Amazon branded product, sold and shipped by Amazon itself of course. The grit on the "8000" was more like 800. Same for the others. For the record, I have a pretty big collection of stones which includes rather pricy items like the 10k chosera but also including some cheap crap like that just to mess with it.
In my opinion, even at $20 these products really aren't worth purchasing. They do work. They do cut very fast. Also dish very fast of course. They need a proper soak, probably 15 minutes at least, before they're ready to be used and will of course make a big old mess as they dish out, and they will dish out immediately. Which is good and bad, it's also why they cut so fast and some of them even provide good feedback. One thing is for sure, the so called grit ratings are a total crapshoot. 3000 is more like a lumpy 300 and the 8000 is literally 800 grit at best.
If you want a proper soaking stone, I suggest, get a Suhero Cerax 1k and call it a day. You can grab a 1k/6k or 1k/3k combo stone from legit resellers on amazon for like $40. Is it worth double the price? Yes. Now you will own an excellent soaking stone combo, and all you'd ever need to maintain pretty much any knife. I really like this product. I also really like the Naniwa traditional line of soaking stones. Either are readily available and excellent choices for a soaking stone.
I think your best bet for a stone to learn on would be something like the 2k shapton pro. I realize it's not super cheap, I guess. It's a much harder splash and go stone that could easily serve as the only stone you'd need. In my opinion it's the best stone in the entire shapton pro line. 3 best shapton pro stones in my experience, only ones you'd need. 320, 2000, either the 8k or the 12k. Both the 1000 and the 1500 sharpening stones are okay too, consider them like course, medium and fine, within the range of a sharpening stone (800-2000 grit). The 320 is great cuz a hard stone like that is a welcome and quite useful thing at a course grit like 320. The 5000 I'm not a big fan of. You're better off with the 8k or the 12k in my opinion. You don't need both, just pick one. 12k is pretty close to 1 micron and I love using this stone to quickly touch up all of my carbon steel blades. I rarely use this for stainless steels but if you have immaculate technique and can execute it it does work. I just prefer to use the much faster cutting, more aggressive cutting, which is a better fit for most stainless, and also imho much better feedback of my shapton glass stones. The glass stones are in my opinion the best splash and go stones on the market bar none. The nanohone, which honestly seems like it's basically just a rebranded shapton glass, is similar. Anyway, I rant on, but a 2k shapton pro is an excellent one and done choice which will cut anything and lasts forever.
Of course if you're not concerned with the price, I've seen 1k choseras on Amazon for like $60. I've seen the 3k on there, which kinda a weird in between grit but a very popular stone for whatever reason, for $80. These are great because they have the vibe of a soaking stone, but they perform basically on the level of a slightly more gentle shapton glass. The gentleness is a pro and con, probably a pro for carbon steel knives and razors and con for harder more wear resistent stainless stuff. The 800k/3000k combo some people promote is a decent way to go for sure. Personally, I'd go 1k or 2k and 5k or 10k. But that's just my preference. I have the 1k, 3k and 10k from this line. Do not soak these stones, even though they seem to take a decent amount of water, you will wreck them if you soak it.